Synthesis, Analysis and Modification of Microgels with ...

Synthesis, Analysis and Modification

of Microgels with Functional

Oligoglycidol Comonomers

Der Fakultät für Naturwissenschaften der Rheinisch-Westfälischen Technischen Hochschule Aachen

vorgelegte Dissertation zur Erlangung des akademischen Grades eines Doktors der

Naturwissenschaften

Vorgelegt von

Diplom-Chemiker

Christian Willems

Aus

Neuwied

Berichter:

Universitätsprofessor Dr. rer. nat. Andrij Pich

Universitätsprofessor Dr. rer. nat. Martin Möller

Tag der mündlichen Prüfung: 06.06.2017

Diese Dissertation ist auf den Internetseiten der Universitätsbibliothek online verfügbar.

III

The most exciting phrase in science, the one that heralds new discoveries, is not “Eureka!” but

“That´s funny…”

- Isaac Asimov

IV

Table of Contents

1. Motivation and Aim of the Work 1

2. General Experimental Part and Instrumental Analysis 4

3. Synthesis and Characterization of Polyvinylcaprolactam Microgels

Functionalized with Oligoglycidol Macromonomers 8

3.1 State of the Art 8

3.2 Aim 18

3.3 Experimental Part 19

3.4 Results and Discussion 29

3.5 Summary and Outlook 55

3.6 Literature 56

3.7 Appendix 61

4. Functionalization of PVCL/Oligoglycidol Microgels 63


4.2 Aim 65




4.6 Literature 86

5. Modification of the Microgel Surface with Polymer Brushes 88


5.2 Aim 93



5.4.1 Grafting-From Polymerization on Microgels by

Cerium Induced Redox Polymerization 108

5.4.2 Grafting-from Single-Electron-Transfer Polymerization 128


5.6 Literature 138

6. Summary 141

7. Nomenclature 144

Danksagung 147

Schlusserklärung 149

1

1. Motivation and Aim of the Work

Microgels are crosslinked colloidal polymer networks which find a useful application in many

different areas. They can be used as additives for functional coatings, drug delivery agents or

catalyst carriers. [1-3] This wide range of microgel applicability is ensured by the combination

of chemical functionality and ability to respond to changes in the environment. Microgels can

change their volume and density as response to external stimuli such as temperature, pH, ionic

strength, etc. [4-6] This intrinsic property can be further tuned to accommodate different

applications by introducing specific functional groups in the microgel structure. The real

challenge lies in the control over the amount and distribution of functional groups in the

microgel structure. For many applications it is important that the functional groups are located

in the microgel shell so as to guarantee an easy availability to other molecules or surfaces. Since

the microgel consists of a loose polymer network with a fuzzy surface, it is difficult to fix

functional groups at the periphery, as they can be distributed throughout the whole microgel

network.

The aim of this work is to develop new routes for the tailored surface decoration of microgels

by using oligoglycidol macromonomers. Oligoglycidol macromonomers exhibit a

polymerisable group that ensures their covalent attachment to microgels. Since they are

amphiphilic they will be located predominantly on the microgel surface, which makes them

more accessible for further modifications. [7] The presence of OH groups in the macromonomer

structure can be used to integrate different functionalities by post-modification processes.

Oligoglycidol macromonomers grafted on the microgel surface will provide efficient sterical

stabilization in aqueous media.

The specific focus of this work was on: a) the synthesis of oligoglycidol macromonomers with

controlled architecture and chemical structure; b) the synthesis of microgels with a controlled

amount of oligoglycidol macromonomers on the surface; c) the postmodification of

oligoglycidol-modified microgels by integration of various functional groups or polymer

chains.

This work is divided in three parts.

In the first part, N-vinylcaprolactam and oligoglycidol macromonomers were copolymerized in

a free radical precipitation polymerization to synthesize microgels with oligoglycidol shells.

Macromonomers with variable molecular weights were synthesized by using ethoxy ethyl

2

glycidyl ether in an anionic polymerization and subsequent deprotection of the OH groups. The

synthesis of the microgel by precipitation polymerization was investigated to determine the

incorporation efficiency and localization of oligoglycidol macromonomers in microgels.

Synthesized microgels were systematically characterized to evaluate the effect of the

comonomer type and amount on the microgel morphology, structure and behavior in aqueous

solutions.

The second part concerns the functionalization of the microgels with functional groups. Since

OH groups of oligoglycidol chains can be easily further modified, it was demonstrated that

various functional groups such as allyl, vinyl sulfonate- or thiol groups can be integrated into

the microgel shell. Modified microgels were analyzed to determine the change of their chemical

structure and properties.

The third part concerns the decoration of oligoglycidol-modified microgels with polymer brush-

like shells by polymerization of several monomers initiated from the microgel surface (grafting-

from). Two types of grafting-from polymerization processes were studied: a) a cerium salt

induced redox polymerization and b) the single-electron transfer living radical polymerization.

Different monomers were used and tested and the reaction conditions were optimized.

3

1.1 Literature

[1] Bradna, P.; Stern, P.; Quadrat, O.; Snuparek, J. Colloid Polym. Sci. 1995, 273, 324-330.

[2] Das, M.; Sanson, N.; Fava, D.; Kumacheva, E. Langmuir 2007, 23, 196-201.

[3] Schunicht, C.; Biffis, A.; Wulft, G. Tetrahedron 2000, 56, 1693-1699.

[4] Otake, K.; Inomata, H.; Konno, M.; Saito, S. Macromolecules 1990, 23, 283-289.

[5] Makhaeva, E.E.; Thanh, L. T. M.; Starodoubtsev, S. G.; Khoklov, A. R. Macromol.

Chem.Phys. 1996, 197, 1973-1982.

[6] Dupin, D.; Fujii, S.; Armes, S. P. Langmuir 2006, 22, 3381-3387.

[7] Mendrek, A.; Mendrek, S., Adler, H.-J.; Dworak, A.; Kuckling Polymer, 2010, 51, 342-

354.

4

2. General Experimental Part and Instrumental Analysis

Chemicals

If not stated otherwise the listed chemicals were used without further purification.

Table 2.1. List of chemicals used in this work.

Vinyl benzyl chloride Sigma-Aldrich

Potassium acetate Sigma-Aldrich

Hydrochinon Sigma-Aldrich

Na2SO4 VWR

NaOH KMF Opti Chem

Ethyl vinyl ether Fluka

Para-toluene sulfonic acid Sigma-Aldrich

Glycidol Sigma-Aldrich

Ethanolamine Sigma-Aldrich

Methacryloyl chloride Sigma-Aldrich

NaHCO3 VWR

CaH2 Sigma-Aldrich

Silica gel Sigma-Aldrich

1M Potassium-tert-butoxide solution in THF Sigma-Aldrich

Hydrochloric acid VWR

N-vinylcaprolactam Sigma-Aldrich

N,N`-methylenebisacrylamide Sigma-Aldrich

2,2`-Azobis[2-methyl-propionamidine]

dihydrochloride

Sigma-Aldrich

Tetrahydrofuran VWR

Dimethylsulfoxide Sigma-Aldrich

Dimethylformamide Merck millipore

Chloroform VWR

Ethanol Sigma-Aldrich

5

Table 2.1. List of chemicals used in this work (continued).

Allyl bromide Sigma-Aldrich

Methanol VWR

Dichloromethan Sigma Aldrich

Potassium iodide Sigma-Aldrich

Triethylamine Sigma-Aldrich

2-Chloroethane sulfonyl chloride (CSC) Alfa Aesar

Dicyclohexylcarbodiimide (DCC) Sigma-Aldrich

Dimethylaminopyridine (DMAP) Sigma-Aldrich

3,3´-Dithiodipropionic acid (DTPA) Sigma-Aldrich

Dithiothreitol (DTT) Sigma-Aldrich

Phosphate buffered saline Sigma-Aldrich

Ceric ammonium nitrate (CAN) Sigma-Aldrich

Di (ethylene glycol) ethyl ether acrylate

(DEGA)

Sigma-Aldrich

2-Methoxy ethyl acrylate (MEA) Sigma-Aldrich

Nitric acid (65%) VWR Chemicals

[2-(Methacryloyloxy) ethyl]-dimethyl (3-

sulfopropyl) ammonium hydroxide

(sulfobetain-1)

Sigma-Aldrich

[2-(Methacryloylamino) ethyl]-dimethyl (3-

sulfopropyl) ammonium hydroxide

(sulfobetain-2)

Sigma-Aldrich

Sodium 4-styrenesulfonate (SSA) Sigma-Aldrich

1-Vinyl imidazole Sigma-Aldrich

N-isopropyl acryl amide (NIPAAM) Sigma-Aldrich

Acryl nitrile Sigma-Aldrich

Copper wire -

CuBr2 Sigma-Aldrich

2-Bromo propionyl bromide Sigma-Aldrich

Hydrazine hydrate Sigma-Aldrich

ME6TREN Sigma-Aldrich

6

N-Vinylcaprolactam (VCL) was purified by distillation under vacuum. Glycidol was dried with

CaH2 and purified by distillation under vacuum.

The solvents dimethylsulfoxide (DMSO), dimethylformamide (DMF), dichloromethane

(DCM), tetrahydrofuran (THF) and ethanol were stored under a nitrogen atmosphere over

molecular sieves (4 Å). Potassium-tert-butoxide solution was stored under a nitrogen

atmosphere.

Analytical Instrumentation

NMR spectra were measured using a Bruker DPX-400 FT-NMR spectrometer at 400 MHz.

Samples were prepared by dissolving 50 mg of the sample in 1 mL of the deuterated solvent.

The chemical shift is indicated in parts per million (ppm). The samples were analyzed using the

software MestReC 4.9.

Transversal relaxation measurements were performed using an AV700 NMR spectrometer at a

proton frequency of 700.2378 MHz. Samples were prepared by dissolving 20 mg in 0.8 mL

deuterated water. The transverse magnetization relaxation was measured using the classical

Hahn-echo experiment, 900x -t – 1800

x – t – Hahn echo – (acquisition), where t is the echo time.

Chromatographic measurements were done using size exclusion chromatography (SEC). For

measurements performed with THF as the eluent, a high pressure liquid chromatography pump

(ERC 6420) and a refractive index detector (WGE Dr. Bures ETA 2020) were used at a

temperature of 30°C. The flow rate of the eluent was 1.0 mL/min. Four columns with a MZ-

DVB gel were applied.

For measurements performed with DMF as eluent, a Bischoff HPLC high pressure liquid

chromatography compact pump with an RI Jasco RI-2031 plus detector was used. Three

columns with PSS GRAM gel were applied. The DMF contained 1 mg/mL LiBr.

The length of each column for THF and DMF measurements was 300mm while the diameter

was 8 mm. The diameter of the gel particles was 5 µm with pore widths of 50, 100, 1000 and

10000 Å. Poly (methyl methacrylate) or polystyrene was used as a standard to achieve a

calibration. The results were analyzed using the software WinGPC unity.

Dynamic light scattering measurements were done in seral water as solvent. Single dynamic

light scattering measurements were performed using an ALV/LSE-5004 spectrometer with an

ALV-5000/EPP multiple digital time correlator and the laser goniometry system ALV/CGS-8F

with a helium/neon laser (Uniphase 1145P, output power: 22mW, wavelength: 632.8 nm) as a

light source. Unless otherwise noted, the measurements were taken at an angle of 90°.

7

Dynamic light scattering measurements at different temperatures were performed using the

Zetasizer Nano ZS. Measurements were taken at an angle of 173°.

Field-Flow Fractionation measurements were performed using the AF 2000 MT separation

system by Postnova Analytics. The microgels were dispersed in deionized water and measured

at a concentration of 1 mg/mL. Regenerated Cellulose was used as a membrane.

Surface tension measurements were performed using a DSA instrument (Krüss).

Macromonomers were measured in water by applying the pendant drop method at an air/liquid

interface. Measurements were performed at room temperature with different macromonomer

concentrations.

Transmission electron microscopy (TEM) measurements were performed on two different

machines. One was the Zeiss LibraTM 120 (Carl Zeiss, Oberkochen, Germany). The electron

beam accelerating voltage was set at 120 kV. The second one was the Hitachi UHR-FE-SEM

SU 9000 (Hitachi). The acceleration voltage was 30 kV and the measurements were performed

in BFSTEM mode. A drop of the sample was trickled on a piece of Formvar and carbon-coated

copper grid. Before being placed into the TEM specimen holder, the copper grid was air-dried

under ambient conditions.

Sedimentation velocity measurements were performed using a Lumifuge and analyzed with the

program SEPView 6. The sedimentation velocity was calculated for a rotation speed of 2000

rpm.

The polymerization heat was measured in a reaction calorimeter by using a RCE1 high

performance Thermostat in an RTCal Glass reactor. Analysis was done with the program

iControl RC1e.

The syntheses of the microgels and their further treatment can be found in the respective

chapters.

8

3. Synthesis and Characterization of Polyvinylcapro-

lactam Microgels functionalized with Oligoglycidol

Macromonomers

3.1 State of the Art

Microgels

Microgels are colloidal particles, made up of polymer chains, which are crosslinked. The

polymer is usually able to form hydrogen bonds with the solvent. As a result, the microgels are

highly porous and rather soft and contain a high amount of solvent.

An exact definition for microgels is not easy to make, so it is usually said that they are spherical

particles with a size ranging from a few nanometers to 1000 micrometers which are able to take

up a lot of solvent. [1] Microgels were first prepared by Staudinger and Husemann in 1935 and

were comprised of polydivinylbenzene which could be dispersed in organic solvents like

benzene. [2]

Aqueous microgels are an important subgroup. They are porous and are filled with water.

Because of the crosslinker, they are not dissolved in water, but they form stable dispersions in

water. Because of the strong polymer/water hydrogen bonds the attractive van-der-Waals

interactions of the microgels are minimized. [3] The polymer chains are more inclined to develop

hydrogen bonds with water, as opposed to secondary valence bonds with each other. The

amount of water, which is contained in the microgel is dependent on the polymer/polymer and

the polymer/water interactions and the crosslinking density. Those interactions are different,

depending on the polymer. [4] But they can also be influenced, by changing the outside

conditions, such as the temperature, the pH-value, the ionic strength of the dispersion, the

strength of a magnetic field or the wavelength of incoming light. [5-10] Polyvinylcaprolactam

(PVCL)-microgels are a good example for temperature sensitive microgels. If the temperature

is increased above the volume phase transition temperature (VPTT = analogous to the lower

critical solution temperature (LCST) of water soluble polymers), the hydrophobic

polymer/polymer interactions increase, which in turn leads to the expulsion of water out of the

colloidal network. The polymer develops secondary valence bonds with each other. As a

consequence the microgels shrink. [11] This is illustrated in figure 3.1.

9

Figure 3.1. Temperature sensitive behavior of a microgel.

The swollen microgels below the VPTT are similar to a statistical coil, whereas at temperatures

above the VPTT, they have a more spherical shape. [12]

Polymers, which show temperature sensitivity and can be synthesized to form microgels are

poly (N-isopropylacrylamide) (PNIPAAM), poly (N-isopropylmethacrylamide) or poly (N-

vinylcaprolactam). [4, 13]

As mentioned above, some microgels are not only responsive to changes in the temperature,

but to other changes in the environment as well. For example the copolymerization of VCL

with 4-vinylimidazole leads to pH-sensitive microgels. The imidazole group can be protonated,

so that the microgels contain charged groups, which repel each other. As a consequence, the

size increases at low pH values. [14]

Depending on the chemical structure, it is possible to synthesize microgels, which are

susceptible to a number of different stimuli, like temperature, pH or ionic strength of the

solution.

Synthesis of Microgels

There are several methods to prepare microgels. They can be synthesized by crosslinking

polymers either by creating covalent bonds between the polymer chains or through the

development of electrostatic interactions. They can also be produced via free radical or

controlled radical polymerization, which can be done as a microemulsion or a precipitation

polymerization.

Especially the precipitation polymerization is a simple and common way to produce microgels

composed of VCL or NIPAAM. The underlying theory is that the monomer is soluble in the

solvent, while the resulting polymer is insoluble so that it precipitates. A precipitation

polymerization works best in a solvent with a high dielectric constant, such as water.

T > VPTT

T < VPTT

10

Additionally, an ionic initiator should be used. A scheme of this method is presented in figure

3.2. [11]

Figure 3.2. Schematic representation of the particle growth process in a precipitation

polymerization. [1]

The monomer, crosslinker and a cationic initiator are dissolved in water at a temperature of 50

to 70°C. The monomers start to polymerize and form small oligoradicals which grow until they

reach a critical chain length. Because the temperature is above the LCST for the formed polymer

chains, they start to precipitate from the solvent and form precursor particles. There are now

two competing growth mechanisms in the polymerization. First, the chains continue to grow by

further polymerization of the monomer in the mixture. In addition, the precursor particles also

aggregate with each other via crosslinking and larger particles are gradually formed. The

collapsed particles still contain a lot of water. At a certain critical size, the aggregation is

hindered by the electrostatic interactions between the positive charges in the microgels, which

come from the cationic initiator fragments. After reducing the temperature below the VPTT,

the water enters the colloidal network and microgels are formed. They are sterically stabilized

through hydrogen bonding between the water and the polymer. A disadvantage of the

precipitation polymerization is the control of the size, since it is usually not possible to

synthesize microgels with a size smaller than 50 nm without a further stabilizing agent. There

are not enough charged initiator fragments to stabilize many small particles. [11]

To synthesize monomodal microgels, surfactants are often used. The surfactants stabilize the

precursor particles and prevent their aggregation. When the aggregation gets inhibited, the

Oligoradicals Precursor particles

Collapsed particles

Microgels

T<VPTT

T>VPTT

11

polymer chains only grow via normal polymerization of the monomers. The growth is more

evenly and the dispersity decreases. This also leads to smaller particles, since the aggregation

would lead to less, larger precursor agglomerates, which is now inhibited. [15] The size and

properties of the microgels can be easily controlled by changes in the amount and type of

crosslinker, initiator, surfactant and changes in the temperature or the stirring rate of the reaction

solution. [15-24] A comonomer can also be introduced during the polymerization

The swelling properties are directly connected to the internal microgel structure. The

crosslinker is usually not evenly distributed throughout the microgel, but is more concentrated

in the core and less in the shell. This is likely because the addition of a crosslinker leads to a

strong increase in the polymer weight by connecting polymer chains with each other, which in

turn quickly decreases its solubility in water. [25]

Two different structures have been suggested for microgels, which are shown in figure 3.3.

Figure 3.3. Schematic representation for two possible morphologies for microgels. [26]

The first idea is that the microgels are comprised of several smaller particles, which have

aggregated during the polymerization process. The second idea suggests a model, where a core-

shell system is developed, with a highly crosslinked core and a less crosslinked shell. Since

these are two idealized forms, it is probable, that the real structure is a mixture between the two

models. [26, 27]

12

Synthesis of Microgels by Copolymerization

The introduction of two monomers in microgels leads to a variety of properties. They can

influence the size and change the colloidal stability of the particles. In addition, they can also

introduce new functional groups into the system.

As stated above, the copolymerization of VCL and N-vinylimidazole (VIm) can lead to pH

sensitive microgels, while still retaining its temperature sensitive properties.

Microgels, which consist of NIPAAM and acrylic acid, show a sensitivity towards temperature,

pH and electrolyte concentration. They also show a change in their swelling behavior and a

change in the VPTT. [28]

By choosing aminoethyl methacrylate hydrochloride as a comonomer in the polymerization of

NIPAAM, it was possible to synthesize cationic microgels, which show a higher VPTT and

smaller size than common PNIPAAM microgels, because the cationic charge leads to a better

stabilization of the precursor particles. [29]

Comonomers can also lead to changes in the overall colloidal network structure. The

copolymerization of VCL and glycidyl methacrylate can lead to so-called core-shell structures.

The methacrylate is more hydrophobic and reacts faster than the VCL, which leads to a core,

which is composed mostly of the acrylate, while the shell is composed of VCL. [30]

Schachschal et al. could show that the copolymerization of VCL, dimethyl itaconate (DMI) and

N-vinylimidazole (VIm) leads to microgels, where the DMI is mainly located in the core and

the VIm is located in the shell. It can be hydrolyzed which leads to negatively charged

carboxylic acid groups so that the microgel ultimately possess an anionic core and a cationic

shell. The temperature sensitivity directly correlates with the pH value of the surrounding

solvent. [31]

PCVL/acetoacetoxyethyl methacrylate (AAEM) microgels, synthesized by Pich et al., contain

the AAEM in the core and are less temperature sensitive than pure PVCL microgels. [13]

Another way of creating core-shell microgels is based on sequential polymerization. The

polymerization of the first monomer forms the core while the addition of the second monomer

leads to the formation of the shell. [32-36]

Reactive macromonomers are a subgroup of monomers. The oligomeric or polymeric chain

determines the physical properties of the molecule. The head-groups are acrylate or vinyl

groups which can be copolymerized with other monomers or with each other to form new kinds

of polymers.

13

Copolymers, comprised of poly (ethylene glycol) and poly (lactic acid) lead to microgels which

are dispersible in hydrophilic and hydrophobic solvents. The poly (ethylene glycol) (PEG) part

is located in the shell and the microgels show good biocompatibility. [37]

PH-sensitive microgels with steric stabilization were prepared by the copolymerization of 2-

(diethylaminoethyl) methacrylate or 2-(diisopropylaminoethyl) methacrylate, with poly

(ethylene glycol) methacrylate (PEGMA) as a comonomer. It was shown that the PEGMA leads

to a higher colloidal stability of the microgels and inhibits flocculation during changes in the

pH-value of the dispersion. The steric stabilization was shown to provide superior stabilization

than charge or surface stabilization. [38]

PEGMA was also used as comonomer for VCL and acetoacetoxyethyl methacrylate (AAEM).

The resulting microgels are smaller, show a lower dispersity, a higher colloidal stability and

lower temperature sensitivity than microgels without the macromonomer. These changed

properties are directly proportional to the amount of comonomer used and the length of the PEG

tail. Since the macromonomer consists of a hydrophilic tail and a hydrophobic head, it tends to

act as a surfactant in water by stabilizing the more hydrophobic monomer during the

polymerization. A higher amount of PEGMA in the polymerization leads to more monomer

droplets which lead to more regular particles. It takes over the role of a surfactant but does not

have to be removed from the finished product. The enhanced colloidal stability is because of

steric stabilization, since the PEGMA is mainly located in the microgel shell. The resulting

particles have a more narrow size distribution than those, which have been synthesized in the

presence of sodium dodecyl sulfate as the stabilizing agent. In addition, functional OH groups

could be introduced into the microgel which now can be further functionalized. [39]

Polyglycidol

PEG is a hydrophilic building block with OH-groups at the chain end that can be further

functionalized. Polyglycidol (PG) can be used as alternative hydrophilic building block with

OH-groups in every repeating unit. It is a hydrophilic biocompatible polymer. [40] Figure 3.4

shows the glycidol monomer and the corresponding polymer.

Figure 3.4. Schematic description of glycidol and the corresponding polymer.

14

Polyglycidol is prepared by anionic polymerization. The direct polymerization of the glycidol

monomer leads to branched polymers, as is shown in figure 3.5. [41]

Figure 3.5. Functional polyglycidols obtained by post-polymerization modification of hydroxyl

side groups. [40]

To prepare linear polyglycidol the hydroxyl group of glycidol has to be temporally protected

(figure 3.6).

Figure 3.6. Glycidol, shown with different protective groups.

15

There are several options to protect glycidol: By etherification or acetalization. Tert-butylether

and allylether groups are easily formed but difficult to remove. Acetal groups are introduced

with ethyl-vinylether and can be easily removed after the polymerization under acidic

conditions. [42-47] The protected monomer ethoxyethyl glycidyl ether (EEGE) is polymerized in

an anionic polymerization and the ethoxyethyl protection group is subsequently removed. As

with PEG, polyglycidol is biocompatible. This makes it interesting for applications in medicine.

The many OH-groups can be modified with several different functional groups. Figure 3.7 gives

a brief overview of the possible modifications with different functional groups. [48]

Figure 3.7. Functional polyglycidols obtained by post-polymerization modification of hydroxyl

side groups. [48]

16

Because of its biocompatibility and ability to prevent unspecified protein absorption,

polyglycidol can be used in coatings for implants. [49] It is also often used as a macromonomer.

Oligoglycidol Macromonomers

Oligoglycidol (OG) macromonomers need a polymerizable group, to be copolymerized with

other vinylic monomers. The double bond can be introduced into the molecule via post- or

premodification.

Mostly, oligoglycidol macromonomers are used in combination with hydrophobic groups, so

that they possess amphiphilic properties. Because of this behavior, they can be easily

polymerized in water as opposed to organic solvents, where the degree of polymerization is

low, because of steric effects. [50, 51]

Because of their hydrophilicity they can be used to synthesize modified polystyrene (PS)

particles which form a stable dispersion in water. Typically, the hydrophobic parts of the

particle are located in the core while the more hydrophilic glycidol parts of the macromonomers

form the outer shell. The microspheres can be used in medical diagnostics because the

oligoglycidol on the surface protects them from unspecified protein adsorption. [52-54]

Synthesized PS/OG particles where the OG chains are functionalized with sulfate end groups

could be used to quantitatively determine Heliobacter pylori in the blood serum. H. pylori

antigens were immobilized on them and their electrophoretic mobility was strongly dependent

on the amount of H. pylori antibodies which bind to the antigen. [55]

Because of their high uniformity those particles can also be used as high-quality photonic

crystals. [56]

It has been observed that OG-macromonomer coated surfaces prevent the absorption of anti-

bovine serum albumin. [49] On the other hand, proteins can be covalently bound through

modification of the hydroxyl groups at the surface. It has been shown that proteins stay

biologically active after the binding process. [57]

Macromonomers can also be polymerized to form polymacromonomers which have a star- or

a brush-like microstructure and can be used in a multitude of ways, e.g. as impact resistant

materials. [58] Such brushes can also be modified to show temperature sensitivity and could be

used as nanoreactors. [59]

17

Applications of Microgels

Microgels find many applications in different areas, such as biology, medicine or mechanics.

Their dispersions can be used as automotive surface coatings because of their shear thinning

properties. [60] The microgels have a high contact surface and can be used as catalysts. [61-63]

Because of the high biocompatibility of some microgels, such as the ones based on PNIPAAM,

there are some applications in the field of biotechnology. For example, they can be used as

coatings for implants which are then used inside the human body to prevent the unspecified

protein absorption on the surface. [64]

Wang et al. synthesized PVCL microgels with methacrylic acid and poly (ethylene glycol)

methyl ether methacrylate as comonomer and N,N-bis (acryloyl) cystamine as a crosslinker.

The microgel can encapsulate doxorubicin and shows a stimuli-triggered drug release in an

acidic or reducing medium. The loaded microgel is non-toxic and shows an efficient anti-tumor

activity to HeLa cells. [65]

Microgels can be loaded with Ag nano particles which can then in turn be released and can act

as effective bacteria killers. [66]

Since the microgel size is directly dependent to an outside stimulus, such as the pH value or the

temperature, they are ideal as sensors or nano switches.

Yasui et al. developed a system where PNIPAAM chains which were functionalized with

Trypsin were anchored to a surface. While the enzyme is surrounded by the PNIPAAM at room

temperature, the chains contract when the temperature is raised so that the enzyme is free.

Consequently, the activity of the enzyme increases. [67]

Microgels can be used to transport active compounds to specific targets. Das et al. could show,

that they could be loaded with gold nano particles which can be released again if they are

irradiated by infrared light. Since infrared light can reach deeper human tissue, such a system

is ideal for targeted release in the human body. [68]

Because of their porosity they can in turn also be used as filtration systems. [69]

18

3.2 Aim

To synthesize pure N-vinylcaprolactam microgels with a low dispersity it is usually necessary

to add a surfactant during the microgel synthesis which is difficult to remove afterwards. In

addition, the microgels tend to aggregate at elevated temperatures which presents a bigger

obstacle in their application as temperature sensitive materials. The usage of surfactants can be

avoided by using a so called surfmer (surfactant and monomer), which acts as a surfactant

during the synthesis and gets incorporated into the nanogel like a comonomer.

In this chapter, the precipitation copolymerization of VCL with different oligoglycidol

macromonomers is presented and the formation of surfmers is analyzed. Several

macromonomers were used that differ in the number of glycidol repeating units. They are

shown in figure 3.8.

Figure 3.8. Schematic representation of the used macromonomers.

It is known that incorporation of PEG macromonomers can greatly enhance the colloidal

stability of microgels. In addition, the size can be tuned by the amount of macromonomer used.

The same effect is to be expected, when using oligoglycidol macromonomers. In addition, the

latter have the advantage of possessing several OH groups per molecule as opposed to one OH

group per PEG molecule. OH groups can be easily modified with other functional groups to

synthesize microgels with new properties. It is possible that the comonomers act as surfactants

which prevent the aggregation of microgels at elevated temperatures.

The aim is to synthesize microgel dispersions which have a defined and tunable size and which

are colloidally stable without the use of a conventional surfactant.

19

3.3 Experimental Part

Synthesis of Vinyl Benzyl Alcohol (VBA)

Vinyl benzyl chloride (12.47 mL, 13.51 g, 0.09 mol) and potassium acetate (10.00 g, 0.10 mol)

are dissolved in dimethylsulfoxide (30 mL) and a small amount of hydrochinon is added. The

solution is stirred for 2 days at 40°C and subsequently filtered. The residue is extracted with

chloroform and the organic phase is washed three times with distilled water (100 mL). The

organic phase is dried with Na2SO4 and filtered. The solvent is removed by distillation and dried

in vacuo. The yellow liquid is now mixed with a solution of NaOH (6.25 g, 0.16 mol) in

H2O/ethanol (6.25 mL/40 mL). After the addition of a small amount of hydrochinon the solution

is stirred under reflux at 110°C for 90 minutes. The resulting suspension is filtrated and

extracted with chloroform. The organic phase is washed three times with distilled water (100

mL) and dried with Na2SO4. The solvent is subsequently removed in vacuo. The resulting liquid

is purified by fractional distillation at 110°C under reduced pressure and the product is received

as a clear liquid.

1H-NMR (DMSO):

δ (ppm) = 4.58 (d, 2H, H-7), 5.22 (d, 1H, H-1), 5.30 (t, 1H, OH), 5.81 (d, 1H, H1), 6.75 (dd,

1H, H-2), 7.36 (2H, H-5), 7.48 (d, 2H, H-4).

13C-NMR (DMSO):

δ (ppm) = 62.8 (C-7), 113.4 (C-1), 125.9 (C-4), 126.7 (C-5), 135.6 (C-3), 136.5 (C-2), 142.3

(C-6).

20

Synthesis of Hydroxyethyl Methacrylamide (HAM)

Ethanolamine is dissolved in chloroform and a small amount of hydroquinone is added. The

solution is cooled down to 0°C. A solution of methacryloyl chloride in chloroform is now

slowly added. The reaction is stirred at 0°C for 30 minutes and stirred at room temperature

overnight. The mixture is filtered and the solvent is removed by distillation. The residue is

purified by column chromatography on silica gel. A solvent a mixture of chloroform and

methanol (4:1) is used. The solvent is removed by distillation and the product is received as a

yellow liquid.

1H-NMR (CDCl3):

δ (ppm) = 1.85 (s, 3H H-1), 3.20 (q, 2H, H-5), 3.45 (q, 2H, H-6) 4.70 (t, 1H, OH), 5.30 (s, 1H,

H-2), 5.66 (s, 1H, H-2), 7.82 (s, 1H, NH).

13C-NMR (CDCl3);

δ (ppm) = 16.5 (C-1), 41.8 (C-5), 59.7 (C-6), 118.9 (C-2), 139.8 (C-3), 167.7 (C-4).

Synthesis of Ethoxyethyl Glycidyl Ether [70]

Ethyl vinyl ether (1.00 L, 753.00 g, 10.44 mol) is mixed with glycidol (178.57 mL, 200.00 g,

2.70 mol) and cooled down to 0°C. Slowly, p-toluene sulfonic acid (5.00 g, 0.03 mol) is added

under stirring. Attention is paid to the fact, that the temperature of the solution does not exceed

10°C. After the whole amount of p-toluene sulfonic acid is added, the reaction mixture is stirred

for 30 minutes at 0°C and for further 5 hours at room temperature. The clear solution is washed

three times with a saturated NaHCO3-solution, dried with Na2SO4 and filtered. The filtrate is

then purified by fractional distillation under reduced pressure at 80°C and the product is left as

21

a clear liquid which is stirred over night with CaH2. DRY EEGE is isolated by condensation

into a Schlenk flask with molar sieve.

1H-NMR (CDCl3):

δ (ppm) = 1.13 (t, 3H, H-7), 1.25 (t, 3H, H-5), 2.54-2.55 (m, 1H, H-1), 2.73 (t, 1H, H-1), 3.08

(m, 1H, H-2), 3.33-3.77 (m, 4H, H-3, H-6), 4,69 (m, 1H, H-4).

13C-NMR (CDCl3);

δ (ppm) = 15.1 (C-7), 19.7 (C-5), 44.5 (C-1), 50.7 (C-2), 60.8 (C-6), 65.7 (C-3), 99.6 (C-4).

Synthesis of Oligo-EEGE [54]

Vinyl benzyl alcohol (2.89 g, 0.02 mol) is dissolved in dimethylformamide (20 mL). Potassium-

tert-butoxide solution (4.34 mL, 1M in THF) is added and stirred for 30 minutes. Then, tert-

butanol and tetrahydrofuran are removed from the solution under reduced pressure. EEGE is

now slowly added to the solution, along with a small amount of hydrochinon. The reaction is

then heated to 80 °C and stirred overnight. Afterwards the dimethylformamide is removed under

reduced pressure. The product is obtained as a brown viscous liquid.

The synthesis of oligo-EEGE using HAM as a substrate is prepared using the same procedure.

The amount of EEGE added in each approach and the substrate used are listed in table 3.1.

22

Table 3.1. Amount of EEGE used for synthesizing the different macromonomers.

Sample Name Substrate /

g (mol)

Number of EEGE

Repeating Units

Amount EEGE /

g (mol)

VBA-EEGE-6 VBA

2.89 (0.02) 6 18.95 (0.13)

VBA-EEGE-12 VBA

2.89 (0.02) 12 37.90 (0.26)

VBA-EEGE-50 VBA

2.89 (0.02) 50 157.44 (1.05)

HAM-EEGE-12 HAM

2.58 (0.02) 12 37.90 (0.26)

The digit of the sample name stands for the number of EEGE repeating units in the

macromonomer with respect to the molar amount of vinyl benzyl alcohol.

VBA-EEGE-6:

1H-NMR (CDCl3):

δ (ppm) = 1.11 (t, 18H, H-14),1.22 (d, 18H, H-12), 3.32-3.70 (m, 42H, H-8-10, H-13), 4.45 (s,

2H, H-7), 4.62 (m, 6H, H-11), 5.15 (d, 1H, H-1), 5.69 (d, 1H, H-2), 6.62 (dd, 1H, H-3), 7.20 (d,

2H, H-4), 7.29 (d, 2H, H-5).

HAM-EEGE-12:

1H-NMR (DMSO):

δ (ppm) = 1.11 (t, 36H, H-13), 1.22 (d, 36H, H-11), 1.84 (s, 3H, H-1) 3.32-3.70 (m, 88H, H-5-

9, H-12), 4.62 (m, 6H, H-10), 5.33 (d, 1H, H-2), 5.69 (d, 1H, H-2).

Synthesis of Oligo-Glycidol [54]

The EEGE-x samples of the previous synthesis are used for this reaction. The protected

macromonomer is dissolved in tetrahydrofuran (ca. 30 mL per g macromonomer) and

23

concentrated hydrochloric acid is slowly added to the solution (ca. 1.5 mL per g

macromonomer). After 3 hours of intense stirring the THF is decanted and the residue is washed

with THF several times. Afterwards the remaining solvent is removed by distillation and the

residue is redissolved in water. With a 1M NaOH-solution the product solution is neutralized.

The solvent is removed again by distillation and the residue was redissolved in ethanol and

NaCl is filtrated. The solvent is removed again by distillation and the product is left as a brown,

viscous liquid.

The synthesis of oligo-glycidol using HAM as a starter molecule is prepared using the same

procedure. The products obtained by using VBA as a starter molecule are called VBA-x with x

being the number of glycidol repeating units in the macromonomer with respect to the molar

amount of vinyl benzyl alcohol. The product obtained by using HAM as a starter molecule is

called HAM-12 with 12 being the number of glycidol repeating units in the macromonomer

with respect to the molar amount of hydroxyethyl methacrylamide.

VBA-6:

1H-NMR (DMSO):

δ (ppm) = 3.36-3.68 (m, 24H, H-7-10), 5.29 (d, 1H, H-1), 5.90 (d, 1H, H-2), 6.78 (dd, 1H, H-

3), 7.35 (d, 2H, H-4), 7.50 (d, 2H, H-5).

HAM-6:

1H-NMR (DMSO):

δ (ppm) = 1.84 (s, 3H, H-1) 3.32-3.70 (m, 76 H, H-5-9), 5.33 (d, 1H, H-2), 5.69 (d, 1H, H-2).

24

Synthesis of Microgels via Batch Method (Method A)

In a double wall reactor N-vinylcaprolactam (2.09 g, 15.05 mmol), N, N´-methylenebis-

acrylamide (0.05 g, 0.32 mmol) and the appropriate amount of the comonomer (VBA, VBA-6,

VBA-12, VBA-50 or HAM-12) are added (table 3.2 to table 3.4) to distilled water (150.00 mL).

The solution is heated to 70°C and stirred for 30 minutes while it is degassed with nitrogen.

Then 2,2´-azobis (2-methyl-propionamidine) dihydrochloride (0.06 g, 0.22 mmol) is added.

The solution is stirred for two hours during which it becomes turbid. After cooling the microgel

dispersion down to room temperature, it is filled in a dialysis membrane with a pore size of

12,000-14,000 Da and dialyzed against distilled water for at least 3 days. The water is changed

at least 3 times a day. The product is a milky dispersion.

Table 3.2. Amount of oligoglycidol macromonomer VBA-6 used for synthesizing the different

microgels (MVBA-6: 578 g/mol).

Sample name Amount VBA-6 /

mol%

Amount VBA-6 /

g (mmol)

MG-6-0.5-A 0.5 0.043

(0.075)

MG-6-1.0-A 1.0 0.087

(0.150)

MG-6-1.5-A 1.5 0.130

(0.226)

MG-6-2.0-A 2.0 0.174

(0.301)

MG-6-2.5-A 2.5 0.217

(0.376)

MG-6-3.0-A 3.0 0.260

(0.451)

MG-6-3.5-A 3.5 0.303

(0.526)

25

Table 3.3. Amount of oligoglycidol macromonomers VBA-12 and VBA-50 used for

synthesizing the different microgels (MVBA-12: 998 g/mol; MVBA-50: 3847 g/mol).

Sample name

Amount

VBA-12 /

mol%

Amount

VBA-12 /

g (mmol)

Sample name

Amount

VBA-50 /

mol%

Amount

VBA-50 /

g (mmol)

MG-12-0.5-A 0.5 0.075

(0.075) MG-50-0.25-A 0.25

0.145

(0.038)

MG-12-0.75-A 0.75 0.113

(0.113) MG-50-0.35-A 0.35

0.203

(0.053)

MG-12-1.0-A 1.00 0.150

(0.150) MG-50-0.5-A 0.50

0.289

(0.075)

MG-12-1.5-A 1.50 0.225

(0.226) MG-50-0.75-A 0.75

0.434

(0.113)

MG-12-2.0-A 2.00 0.300

(0.301) MG-50-1.0-A 1.00

0.579

(0.150)

MG-6-1.25-A 1.25 0.724

(0.188)

Table 3.4. Amount of comonomers VBA and HAM-12 used for synthesizing the different

microgels (MVBA: 134 g/mol; MHAM-12: 1017 g/mol).

Sample name

Amount

comonomer /

mol%

Amount

comonomer /

g (mmol)

MG-0.5-A 0.5 0.010

(0.075)

MG-2.0-A 2.0 0.040

(0.150)

HAM-12-2.0-A 2.0 0.130

(0.226)

HAM-12-4.0-A 4.0 0.174

(0.301)

The amount of VBA-x used is given as mol% with respect to the molar amount of the VCL

monomer (15.05 mmol). The synthesized microgel samples are further referred to as MG-x-y-

A. X stands for the number of repeating units in the macromonomer whereas y stands for the

amount of macromonomer used in mol%. A means that the microgel was synthesized by batch

synthesis.

26

1H-NMR (D2O):

δ (ppm) = 1.00-2.20 (m, 8H, H-2, H-5), 2.20-2.80 (m, 2H, H-1), 2.80-3.50 (m, 2H, H-3), 3.50-

3.80 (m, varying amounts, H-6, H-7, H-10-13), 4.00-4.58 (m, 1H, H-4), 7.31 (m, 4H, H8, H9).

Synthesis of Microgels via Continuous Feed-Method (Method B)

In a double wall reactor N-vinylcaprolactam (2.09 g, 15.05 mmol) and the appropriate amount

of the oligoglycidol-macromonomer (table 3.5 to table 3.7) is added to distilled water (148 mL).

The solution is heated to 70°C and stirred while being degassed with nitrogen. N, N´-

methylenebisacrylamide (0.05 g, 0.32 mmol) is dissolved in distilled water (2 mL) in a snap

cap vial. After 30 minutes of stirring, azobis (2-methyl-propionamidine) dihydrochloride (0.06

g, 0.22 mmol) was added to the monomer solution. The BIS solution was taken up in a syringe

and added to the reaction solution with a syringe pump. The start and duration of the BIS

addition is listed in the table 3.5 to 3.7. After the addition is complete the reaction is continued

for two hours. After cooling the microgel dispersion down to room temperature, it was filled in

a dialysis membrane with a pore size of 12,000-14,000 Da and dialyzed against distilled water

for at least 3 days. The water was changed at least 3 times a day. The product was a milky

dispersion.

1H-NMR (D2O):

δ (ppm) = 1.00-2.20 (m, 8H, H-2, H-5), 2.20-2.80 (m, 2H, H-1), 2.80-3.50 (m, 2H, H-3), 3.50-


27

Table 3.5. Amount of oligoglycidol macromonomer VBA-6 used for synthesizing the different

microgels (MVBA-6: 578 g/mol).


mol%

Amount VBA-6 /

g (mmol)

Start of BIS

addition / s*

End of BIS

addition / s*

MG-6-0.5-B 0.5 0.043

(0.075) 0 550

MG-6-1.0-B 1.0 0.087

(0.150) 200 700

MG-6-1.5-B 1.5 0.130

(0.226) 250 750

MG-6-2.0-B 2.0 0.174

(0.301) 600 1200

MG-6-2.5-B 2.5 0.217

(0.376)

MG-6-3.0-B 3.0 0.260

(0.451) 800 1400

MG-6-3.5-B 3.5 0.303

(0.526) 850 1450

Table 3.6. Amount of oligoglycidol macromonomer VBA-12 used for synthesizing the

different microgels (MVBA-12: 998 g/mol).


mol%

Amount

VBA-12 /

g (mmol)

Start of BIS

addition / s*

End of BIS

addition / s*

MG-12-0.5-B 0.5 0.075

(0.075) 0 550

MG-12-1.0-B 1.00 0.150

(0.150) 200 700

MG-12-1.5-B 1.50 0.225

(0.226) 300 850

MG-12-2.0-B 2.00 0.300

(0.301) 600 1100

MG-12-3.0-B 3.00 0.450

(0451) 850 1300

28

Table 3.7. Amount of oligoglycidol macromonomer VBA-50 used for synthesizing the

different microgels (MVBA-50: 3847 g/mol).


mol%

Amount VBA-50 /

g (mmol)

Start of BIS

addition / s*

End of BIS

addition / s*

MG-50-0.25-B 0.25 0.145

(0.038) 0 500

MG-50-0.35-B 0.35 0.203

(0.053) 0 500

MG-50-0.5-B 0.50 0.289

(0.075) 0 550

MG-50-0.75-B 0.75 0.434

(0.113) 100 600

MG-50-1.0-B 1.00 0.579

(0.150) 250 750

MG-50-1.25-B 1.25 0.724

(0.188) 360 900

* The start and the end of the crosslinker addition refer to a time of x seconds after the addition of the initiator which is defined

as t=0.

The amount of VBA-x used is given as mol% with respect to the molar amount of the VCL

monomer (15.05 mmol). The synthesized microgel samples are further referred to as MG-x-y-

B. x stands for the number of repeating units in the macromonomer whereas y stands for the

amount of macromonomer used in mol%. B means that the microgel was synthesized by

continuous feed synthesis.

29

3.4 Results and Discussion

Oligoglycidol macromonomers with different chain lengths were synthesized and

copolymerized with VCL to form microgels. The synthetic process was analyzed and the

properties of different microgels such as size, temperature responsivity and colloidal stability

were determined.

Oligoglycidol Macromonomers

Oligoglycidol macromonomers with different chain lengths were prepared according to a

procedure developed by Sascha Pargen et al. [54] The successful synthesis was proven by 1H-

NMR spectroscopy and by size exclusion chromatography. The results are shown in table 3.8.

Table 3.8. SEC results for the protected and deprotected oligoglycidol macromonomers.

Sample Mn (theoretical) /

g/mol

Mn (GPC) /

g/mol PDI

VBA-EEGE-6 1010 1255 1.11

VBA-EEGE-12 1886 2442 1.07

VBA-EEGE-50 7434 12878 1.07

VBA-6 578 520 1.14

VBA-12 998 806 1.06

VBA-50 3847 4594 1.15

The actual molecular weight of all samples is similar to the theoretical one. They were now

used in the microgel synthesis. All further calculations were made with the theoretical

molecular weights.

Before they can be used in the microgel synthesis they have to be purified extensively. After

washing the macromonomer with THF, pentane and diethyl ether there is still a strong

possibility, that acid is left in the final solution. If this is the case, the usage of this solution in

the microgel synthesis leads to a low yield, because the acid causes hydrolytic degradation of

N-vinylcaprolactam (Scheme 3.1). [71, 72]

30

Scheme 3.1. Hydrolysis of N-vinylcaprolactam in acidic medium. [71]

This scheme was proposed by Ainara Imaz et al. [71] The group states that VCL reacts with the

acid and forms caprolactam and acetaldehyde. To prevent this, the macromonomer solution is

neutralized with NaOH. Afterwards the water is evaporated and the residue is dissolved in

ethanol. The NaCl formed is insoluble in ethanol and can be filtered off.

Since the macromolecules have a hydrophobic head (styrene group) and a hydrophilic tail

(glycidol chain) their surface tension was tested. Figure 3.9 shows the surface tension in

dependence of the macromonomer concentration.

Figure 3.9. Surface tension of different macromonomers in dependence of the concentration.

The surface tension of the macromonomers drops with an increasing concentration. It can be

seen, that this drop is more pronounced if oligoglycidols with shorter chains are added. With

increasing chain length a less pronounced drop in surface tension is observed. With increasing

chain length, the hydrophobic effect of the head group becomes negligible in comparison to the

long tail group.

VCL is only slightly soluble in water at room temperature and can only be dissolved in warm

water. The hypothesis is that the macromonomer head group is oriented towards the VCL in

water, whereas the tail group is oriented outward which leads to hydrophobic domains within

the aqueous solution, containing VCL and PVCL.

50

52

54

56

58

60

62

64

66

68

70

0,05 0,5 5

IFT

/ [

mN

/m]

c / [g/L]

VBA-6

VBA-12

VBA-50

31

A range from 0.05 to 5 g/L of macromonomer was chosen, as this is the range of oligoglycidol

concentration which is used in the synthesis of microgels. The oligoglycidol-macromonomers

are now used as comonomers in a precipitation polymerization with N-vinylcaprolactam.

Analysis of the Microgel Formation Process

PVCL/Oligoglycidol microgels were synthesized via precipitation polymerization, with N,N´-

methylenebisacrylamide as crosslinker and 2,2´-azobis (2-methyl-propionamidine)

dihydrochloride as a water soluble cationic initiator. The formation of the microgels was

analyzed with the help of a calorimeter. The amount of monomer, crosslinker and initiator was

kept constant while the amount of macromonomer was varied. The heat of reaction was

measured as a function of time. Figure 3.10 shows the heat flow during the microgel synthesis

with VCL as a monomer and VBA-6 as a comonomer.

Figure 3.10. Heat flow during the synthesis of PVCL microgels by copolymerization of VCL

and different amounts of VBA-6.

The time of 0 is the point of reaction when the initiator is added. With an increasing amount of

added comonomer the time between initiator addition and the development of heat increases.

This is supported by turbidity measurements (fig. 3.11) which show that with increasing amount

of macromonomer the time for the formation of microgels – the time at which the solution

becomes turbid – increases.

0

1

2

3

4

5

6

0 500 1000 1500

Hea

t F

low

/ W

t / sec

pure PVCL

MG-6-0.5-A

MG-6-1.0-A

MG-6-2.0-A

MG-6-3.0-A

MG-6-3.5-A

32

Figure 3.11. Turbidity measurements during the microgel synthesis. Used macromonomer:

VBA-6.

With pure VCL (without macromonomer) the formation of microgel starts earlier than in the

presence of oligoglycidol.

This means, that the macromonomer has a retarding effect on the microgel formation. In table

3.9 the heat of reaction heat for the formation of microgels as a function of added comonomer

is presented. Polymerization conversion was calculated using the polymerization heat of VCL,

which is 79 kJ/mol. [73]

Table 3.9. Reaction heat and yields for different microgels containing VBA-6.

Amount of VBA-6 /

mol%

Heat of

Polymerization /

kJ

Conversion /

%

Gravimetric yield /

%

0 1.186 99.6 99.0

0.5 1.029 86.5 69.5

1 1.151 96.8 69.4

1.5 1.170 98.6 83.9

2 1.124 91.3 62.7

3 1.098 92.3 79.9

3.5 1.081 90.9 81.0

The gravimetric yield describes the yield which was calculated by determining the amount of

product mass. The conversion is calculated through the reaction heat by comparing the ratio of

0

5

10

15

20

25

30

0 500 1000 1500

Tu

rb

idit

y /

%

t / sec

pure PVCL MG-6-0.5-A

MG-6-1.0-A MG-6-2.0-A

MG-6-3.5-A

33

the reaction heat to the reaction heat of a 100% conversion of VCL monomer which is 1.189

kJ. The reaction heat of the macromonomer was taken as negligible because of the low portion

which is used in the syntheses. Judging from the reaction enthalpy, the conversion of the

monomer is mostly nearly 100%. This proves that the addition of the macromonomer does not

inhibit the microgel formation, but merely retards it.

The gravimetric yield of the reactions was also measured. It was found, that the yield of the

functionalized microgels is significantly lower than from a pure PVCL microgel which does

not contain any glycidol. This leads to the conclusion that the presence of the macromonomers

leads to an increase in the noncrosslinked, soluble sol fraction, which gets washed out during

the purification of the microgel. The change in the yield does not seem to follow a specific

trend. Microgels copolymerized with VBA-12 and VBA-50 show matching results, as shown

in table 3.10.

Table 3.10. Reaction heat and yields for microgels containing VBA-12 or VBA-50.

Amount of

macromonomer /

mol%

Reaction heat /

kJ

Conversion /

%

Gravimetric yield /

%

VBA-12

0 1.186 99.6 99.0

0.5 1.054 88.6 92.3

1 1.075 90.4 74.4

1.5 1.027 86.3 74.3

2 1.140 95.9 63.6

3 1.049 88.2 80.4

VBA-50

0.25 1.150 96.7 71.9

0.35 1.133 95.2 71.5

0.5 1.126 94.7 83.3

0.75 1.040 87.4 61.1

1.00 1.101 92.6 95.0

1.25 1.172 98.5 59.7

Similar to the VBA-6 samples, the other samples show a high conversion, but the gravimetric

yield after the purification is relatively low.

34

It is noticeable, that immediately after the addition of the initiator, there is a small peak, which

is especially noticeable at the synthesis with the pure PVCL and the one with 0.5 mol% VBA-

6. It is assumed, that this peak can be assigned to the crosslinker N,N`-methylenebisacrylamide

(BIS), which polymerizes with a small fraction of the VCL. The presence of comonomer leads

to a retardation of the polymerization of the N-vinylcaprolactam, but the BIS is not affected by

this process. It is assumed, that the macromonomer has the same effect, as a surfactant on the

VCL. It encloses the monomer, so that the water-soluble initiator cannot reach it initially. But

since BIS is more soluble in water than VCL, it is not enclosed by the surfactant and can react

immediately with the initiator. This leads to a microgel, where the core is highly crosslinked,

while the outer part of the shell is only loosely crosslinked.

Influence of the Head Group on the Microgel Formation Process

The influence of the vinyl benzyl alcohol group of the macromonomer was examined. This was

done by performing a microgel synthesis with different amounts of pure vinyl benzyl alcohol.

The results are shown in figure 3.12a. In comparison, the heat flow of microgel syntheses with

0.5 mol% of different comonomers are shown. The results are shown in figure 3.12b.

Figure 3.12. Heat flow as a function of time for the VCL microgel synthesis in the presence of

0.5 and 2.0 mol% vinyl benzyl alcohol (a) and in the presence of 0.5 mol% VBA, VBA-6,

VBA-12 and VBA-50 (b).

It is shown, that the retardation of the reaction directly correlates with the amount of vinyl

benzyl alcohol, which is introduced into the synthesis. A higher amount of VBA leads to a

longer induction period until the main polymerization starts. A comparison with different

0

1

2

3

4

5

6

0 500 1000 1500

Hea

t F

low

/ W

t / sec

MG-0.5-A

MG-2.0-A

0

1

2

3

4

5

6

0 200 400 600 800 1000

Hea

t F

low

/ W

t / sec

MG-0.5-A

MG-6-0.5-A

MG-12-0.5-A

´MG-50-0.5-A

a b

35

macromonomers shows, that the same amount of macromonomer leads to the same induction

period. This means, that the oligoglycidol tail group has no influence on the polymerization

rate.

It is assumed that beside the radical addition to the C, C-double bond a side reaction occurs

leading to a hydrogen transfer reaction from the benzyl position and formation of a stable

radical. Figure 3.13 shows the proposed mechanism for this.

Figure 3.13. Hydrogen transfer side reaction from the benzyl position of the macromonomer

to a growing radical.

The head group functions as a retarder.

Macromonomer Incorporation Efficiency

After the synthesis, the microgels were purified via dialysis and analyzed. Figure 3.14 shows

several 1H-NMR-spectra of a PVCL-microgel without the macromonomer and with 1.0 and 2.0

mol% of VBA-6.

36

Figure 3.14. 1H-NMR spectra of PVCL microgels without macromonomer (top), with 1.0

mol% VBA-6 (middle) and with 2.0 mol% VBA-6 (bottom).

The signals at a chemical shift of 1.44 ppm, 1.98 ppm, 2.94 ppm and 3.94 ppm all can be

assigned to the N-vinylcaprolactam. The signal at 3.30 to 3.38 ppm corresponds to the

oligoglycidol chain. By comparing the intensity of the oligoglycidol signal with the signal at

3.94 ppm, it is possible to calculate the incorporated amount of the macromonomer. Table 3.11

shows the results for all macromonomers in comparison with the theoretically expected amount.

ppm (t1)

1.02.03.04.0

4.4

63

3.9

63

3.9

59

2.9

43

2.1

62

2.1

56

1.9

91

1.4

52

1.4

48

1.0

0

1.8

0

2.3

2

8.1

5

ppm (t1)

1.02.03.04.0

4.4

55

3.9

49

3.3

86

3.3

13

2.9

48

2.1

51

1.9

88

1.4

32

1.4

29

1.0

0

0.4

5

1.8

1

2.1

5

8.5

2

ppm (t1)

1.02.03.04.0

4.4

41

3.9

47

3.3

82

3.3

78

3.3

00

2.9

45

2.1

48

1.9

80

1.4

45

1.0

0

0.7

3

1.6

4

1.9

4

6.5

3

Oligo-

glycidol

37

Table 3.11. List of theoretically expected (Amounttheo) and found (Amountfound) amount of

macromonomer within the microgels prepared. Used macromonomer: VBA-6. Synthesis A.

Amounttheo /

mol%

Amountfound /

mol%

0.5 > 0.9

1 1.5

1.5 1.64

2 2.43

3 3.00

3.5 3.63

The calculated amount of the oligoglycidol roughly corresponds with the theoretical values.

Deviations from the theoretical values are mainly because the oligoglycidol signal and the

signal for a CH2-group at 2.9 ppm overlap, which makes an exact calculation difficult.

Nevertheless, it can be said that the incorporation of the macromonomer is successful. The

found amount of comonomer in the microgel is actually higher than the theoretically expected

one. This can be due to the fact that some noncrosslinked PVCL chains were washed out during

the dialysis of the samples. The results for the microgels synthesized with VBA-12 and VBA-

50 were similar. Specific amounts of oligoglycidol macromonomer can be introduced into the

microgel.

It is now important to know, whether the oligoglycidol macromonomer is located in the shell

or the core of the microgel or if it is evenly distributed throughout the particle. In order to

determine this, a transversal relaxation nuclear magnetization experiment has been done. By

isolating a signal that only corresponds to one specific part of the microgel, in this case the

oligoglycidol and the caprolactam, it is possible to determine the transversal magnetization

decay (T2) for both components. A higher decay means a higher mobility for the corresponding

molecule which in turn means a localization in the shell. [74, 75] The microgel, functionalized

with 2.0 mol% VBA-6 was used for the analysis. For analysis, the peak at 3.38 ppm was chosen

as signal for the oligoglycidol and the peak at 1.44 ppm was chosen for the VCL component.

Figure 3.15 shows the proton NMR transverse relaxation decay for the glycidol- and the VCL-

part of the microgel.

38

Figure 3.15. Transversal relaxation decay for the glycidol (a) and the VCL (b) component of

the microgel. The measurement was done, using a Hahn-echo pulse sequence.

The calculated values for the transverse relaxation times (T2(shell) and T2(core)) and the

corresponding relative coefficients (A(shell) and A(core)) for each component were calculated and

are listed in table 3.12. They are proportional to the number of protons which contribute to the

NMR signal.

Table 3.12. Determined variables for the transverse relaxation time and number of protons

Component A(shell) T2(shell) / ms A(core) T2(core) / ms

VCL 0.78 5.61 0.25 0.19

VBA-6 0.91 14.08 / /

For the VCL component, a biexponential fit gives the best results, whereas for glycidol a

monoexponential fit works best. For VCL, two values for T2 could be determined. This means

that it can be found in the core and the shell of the microgel. For glycidol, one single transverse

relaxation time of 14.08 ms was determined. A higher transverse relaxation time means a higher

mobility for the corresponding molecule which in turn means localization in the shell. The

relaxation time for glycidol is much higher than both values for VCL which means that the

glycidol component is located in the microgel shell. Similar results could be obtained for the

microgels copolymerized with VBA-12 and VBA-50.

0

0,2

0,4

0,6

0,8

1

0 10 20 30 40

Inte

gra

l In

ten

sity

/ A

rb

. U

nit

s

Echo Time / ms

a

0

0,2

0,4

0,6

0,8

1

0 5 10 15 20

Inte

gra

l In

ten

sity

/ A

rb

. U

nit

s

Echo Time / ms

b

39

Properties of N-Vinylcaprolactam/Oligoglycidol Microgels

The number of glycidol repeating units in the comonomer has no influence on the rate of

reaction of the microgels. But it shows a high influence on their size. This is shown in figure

3.16.

Figure 3.16. Size of microgels in dependence of the amount and kind of macromonomer used

in the synthesis. Y stands for the amount of macromonomer used.

With an increasing amount of macromonomer content in the microgel, its size decreases. This

is due to two effects. First, the application of pure VBA leads to a decrease in size. But it is also

noticeable, that the size decreases with an increase in the molecular weight of the glycidol chain.

Microgels, modified with 0.5 mol% VBA-50 are much smaller than the ones with 0.5 mol%

VBA-12 or 0.5 mol% VBA-6. This means, that the head group and the glycidol chain both have

an effect on the hydrodynamic radius. At 2 mol%, the size of PVCL/VBA-microgels is nearly

the same as the size of PVCL/VBA-6 microgels. Because the glycidol side chain is short, its

influence is negligible in comparison to the influence of the vinyl benzyl alcohol group. By

choosing the right amount of macromonomer with the right number of glycidol repeating units,

it is possible, to tune the size of microgels and incorporate a defined amount of hydroxyl groups.

Figure 3.17 shows the size distribution for the samples modified with VBA-6.

0

50

100

150

200

250

300

350

400

450

500

0 0,5 1 1,5 2 2,5 3

rH

/ n

m

Amount macromonomer / mol%

MG-y-A

MG-6-y-A

MG-12-y-A

MG-50-y-A

40

Figure 3.17. Size distribution of microgels prepared from VCL and VBA-6 in different

concentration.

With an increasing amount of VBA-6 (from 0.5 to 2.0 mol%), the dispersity of the microgels

decreases, while at 2.5 mol% of VBA-6 the size distribution increases again. The samples, made

with VBA-12 and VBA-50 show a similar trend, but in addition, there is the formation of

secondary smaller particles at very high concentrations of oligoglycidol, as can be seen in figure

3.18 a and 3.18 b.

Figure 3.18. Size distribution of microgels prepared from VCL and VBA-12 (a) and VBA-50

(b) in different concentration.

It is assumed, that the reduction of the nanogel size is due to the tendency of the

macromonomers to act as surfactants during the synthesis. The glycidol chains provide steric

stabilization, so that the aggregation of the precursor particles is prevented. The more

1 10 100 1.000rH / nm

pure PVCL

MG-6-0.5-A

MG-6-1.0-A

MG-6-1.5-A

MG-6-2.0-A

MG-6-2.5-A

1 10 100 1.000rH / nm

pure PVCL

MG-12-0.5-A

MG-12-0.75-A

MG-12-1.0-A

MG-12-1.5-A

MG-12-2.0-A

1 10 100 1.000rH / nm

pure PVCL

MG-50-0.25-A

MG-50-0.35-A

MG-50-0.5-A

MG-50-0.75-A

MG-50-1.0-A

MG-50-1.25-A

a b

41

macromonomer is used in the copolymerization, the better precursor particles are protected

against aggregation. Scheme 3.2 shows the assumed microgel formation mechanism during the

precipitation polymerization.

Scheme 3.2. Microgel formation process, with (bottom) and without (top) oligoglycidol

macromonomers. [1]

At very high macromonomer content the formation of secondary smaller particles below 50 nm

is favored.

To verify the existence of actual microgel particles, some selected samples were analyzed by

performing transmission electron microscopy (TEM) measurements. They are shown in figure

3.19.

Oligoradicals Precursor particles

Collapsed particles

Microgels

T<VPTT

T>VPTT

T<VPTT

T>VPTT

42

Figure 3.19. TEM images of different PVCL/Oligoglycdiol microgels. a: PVCL without

glycidol; b: MG-6-0.5-A; c: MG-50-0.5-A.

The spherical shape of the microgels could be proven. It is seen that a higher amount of the

oligoglycidol content in the microgel leads to smaller and softer particles, which verifies the

results obtained by DLS measurements.

The modified microgels are temperature sensitive, like the pure PVCL-microgels. Figure 3.20

shows the temperature responsibility of microgels, modified with VBA-6.

Figure 3.20. Hydrodynamic radius of several microgels in dependence of the temperature. Used

samples: MG-6-y-A.

The microgel dispersion concentration for each sample was comparable. Each sample shows a

temperature responsibility. If the pure PVCL microgel is heated above 35 °C then a slight

increase of the hydrodynamic radius is observed. This is due to the agglomeration of some

particles. This behavior is more pronounced at higher concentrations. This agglomeration is

prevented or at least diminished in the samples containing macromonomer. It is hypothesized,

that the oligoglycidol acts as a sterical hindrance for the microgels, so that no or at least a

reduced agglomeration takes place.

0

50

100

150

200

250

300

350

400

15 25 35 45 55

rH

/ n

m

T / °C

pure PVCL

MG-6-0.5-A

MG-6-1.0-A

MG-6-2.0-A

MG-6-3.0-A

43

Samples with VBA-12 and VBA-50 show a similar response, as seen in figure 3.21.

Figure 3.21. Temperature sensitivity of VBA-12 (left) and VBA-50 (right).

With an increase in the macromonomer content of the microgels, it becomes apparent, that the

size difference between swollen and shrunken microgels becomes smaller.

To get a value for the shrinking of the microgel with increasing temperature, the radius of the

swollen microgel at 15 °C was compared with the radius of a collapsed one at 51 °C. In order

to measure the microgels at 51°C the samples were extremely diluted to prevent an aggregation

which could distort the results. Table 3.13 lists the shrinking degrees for all samples.

Table 3.13. Degree of shrinking for microgels prepared by copolymerization of VCL with

VBA-6 (left), VBA-12 (middle) and VBA-50 (right).

Sample rH(51°C)/

rH(15°C) Sample

rH(51°C)/

rH(15°C) Sample

rH(51°C)/

rH(15°C)

Pure PVCL 0.32 Pure PVCL 0.32 Pure PVCL 0.32

MG-6-0.5-A 0.30 MG-12-0.5-A 0.47 MG-50-0.25-A 0.41

MG-6-1.0-A 0.32 MG-12-1.0-A 0.46 MG-50-0.35-A 0.35

MG-6-2.0-A 0.46 MG-12-1.5-A 0.39 MG-50-0.5-A 0.47

MG-6-3.0-A 0.60 MG-12-2.0-A 0.65 MG-0.75-A 0.56

MG-50-1.0-A 0.80

0

50

100

150

200

250

300

350

400

15 25 35 45 55

rH

/ n

m

T / °C

pure PVCL

MG-12-0.5-A

MG-12-1.0-A

MG-12-1.5-A

MG-12-2.0-A

0

50

100

150

200

250

300

350

400

15 25 35 45 55

rH

/ n

mT / °C

pure PVCL

MG-50-0.25-A

MG-50-0.35-A

MG-50-0.5-A

MG-50-0.75-A

MG-50-1.0-A

44

The difference between swollen and shrunken microgels becomes smaller, with an increasing

macromonomer amount. Pure PVCL shrinks to 30% of its size when heated while the samples

MG-6-3.0-A and MG-12-2.0-A only shrink to roughly 60% of their size. Comparing samples

copolymerized with 1.0 mol% of macromonomer the size difference between the swollen and

shrunken microgels decreases.

This is likely due to the following effect. The crosslinker and a small amount of VCL are getting

polymerized first, while the bulk of the monomer gets polymerized later. The later the monomer

starts to polymerize, the more crosslinker is already consumed in the reaction. This leads to

microgels with a strongly crosslinked core and a very loose shell. The crosslinked area is

smaller and the loose VCL chains are more mobile, so they don´t collapse as strongly, as the

crosslinked polymer, while the core becomes more and more rigid which inhibits its ability to

shrink or swell.

The phenomenon cannot be explained by the retardation of the polymerization alone.

Otherwise, the temperature sensitivity for the sample MG-50-1.0-A should be equally to the

sensitivity of the sample MG-6-1.0-A. The second reason is an increase in the hydrophilicity of

the microgel, because of a higher number of hydrophilic groups. At temperatures which are

higher than the VPTT, less water is ejected out of the microgel. The size and the temperature

sensitivity can be tuned to a certain degree.

Additionally, the sedimentation velocity of the microgels was measured with the Lumifuge

which is shown in figure 3.22.

Figure 3.22. Sedimentation velocity of microgels.

0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

0,4

0,45

0 0,5 1 1,5

Sed

imen

tati

on

velo

cit

y / [

µm

/s]

Macromonomer content / mol%

MG-6-A

MG-12-A

MG-50-A

45

All samples were measured at a dispersion concentration of around 11 g/L. The Lumifuge

calculates the sedimentation velocity by measuring the change of transparency of the sample

over time. Not all synthesized samples could be measured, since samples containing a high

amount of glycidol are too transparent for the Lumifuge to obtain results. But it is clear that the

sedimentation velocity decreases with an increasing amount of glycidol in the microgel. This is

due to the increased hydrophilicity and the decreased size of the sample, so that the microgel is

colloidally more stable in water. It is assumed, that microgels which are too transparent to be

tested, are even more stable.

The overall data suggests that there is a limit of macromonomers which can be copolymerized

with VCL. If too much is used during the synthesis, the microgels become too small and show

a high dispersity. In order to solve this, an alternative polymerization method was employed, in

which the crosslinker is continuously added to the reaction medium.

Synthesis of PVCL/Oligoglycidol-Macromonomer-Microgels, with a Continuous

Addition of Crosslinker

It has been shown that the macromonomer retards the polymerization of the VCL while the

crosslinker BIS reacts almost immediately after the initiator addition. The start of the

polymerization of VCL can be pinpointed by analyzing the calorimetric data, which is shown

in figure 3.10. Instead of synthesizing the microgel in a batch procedure using a mixture of all

reagents, in this new procedure the crosslinker BIS is dissolved in distilled water and slowly

added to the reaction mixture with a syringe pump. The addition starts, after the initiator was

added and has initiated the copolymerization of VCL with the macromonomer. By adding the

BIS continuously, it is assumed, that the formed microgel is more evenly crosslinked than

samples in which all reagents are present from the beginning. Figure 3.23 now shows the

hydrodynamic radius of microgels in dependence of the amount of macromonomer.

46

Figure 3.23. Size of microgels in dependence of amount and type of macromonomer. Method

B.

With an increasing amount of macromonomer, the size decreases. However, this decrease is not

nearly as high as with microgels, synthesized with method A. At higher concentrations of the

macromonomer the size stays constant, regardless of the macromonomer content. There are

differences in size between the microgels, synthesized with different macromonomers. It can

be seen, that the size decreases, with an increase in the number of glycidol repeating units per

macromonomer.

For VBA-6 microgels, the size distribution can be seen in figure 3.24.

Figure 3.34. Size distribution of microgels obtained by copolymerization of VCL with VBA-6

(method B).

0

50

100

150

200

250

300

350

400

0 1 2 3

rH

/ n

m

Amount macromonomer / mol%

MG-6-B

MG-12-B

MG-50-B

10 100 1.000

rH /nm

pure PVCL

MG-6-0.5-B

MG-6-1.0-B

MG-6-1.5-B

MG-6-2.0-B

MG-6-2.5-B

MG-6-3.0-B

MG-6-3.5-B

47

The size distribution is still very broad. The dispersity of microgels with the macromonomer is

in most cases higher than the dispersity of the pure PVCL microgel. In addition to the major

population of particles, a second population of smaller particles – around 20 nm – is observed.

This behavior was to be avoided. 1H-NMR spectra of the synthesized samples were done, to

calculate the incorporation efficiency. Table 3.14 shows the found amounts of macromonomer

in comparison with the theoretically expected amount.


macromonomer within the microgels prepared. Used macromonomer: VBA-6. Synthesis B.

Sample Name Amounttheo /

mol%

Amountfound /

mol%

MG-6-0.5-B 0.5 0.73

MG-6-1.0-B 1.0 0.96

MG-6-1.5-B 1.5 1.16

MG-6-2.0-B 2.0 1.16

MG-6-3.0-B 3.0 1.70

MG-6-3.5-B 3.5 1.66

In comparison to method A, the incorporation efficiency is lower in this case. Only a fraction

of the macromonomer was actually incorporated into the microgel. There is a difference

between the amount of oligoglycidol that was theoretically expected and the found amount.

This difference gets higher with an increasing amount of the macromonomer.

In summary it can be concluded, that method B does not result in microgels with predetermined

amounts of VBA-6 in VCL. The reason might be that VBA-6 tends to prevent the

copolymerization of BIS with other monomers in the mixture. In comparison, the size

distribution for the systems with VBA-12 and VBA-50 is shown in figure 3.25.

48

Figure 3.25. Size distribution of microgels obtained by copolymerization of VCL with VBA-

12 (left) and VBA-50 (right).

A much more narrow size distribution can now be observed for both systems. There is no

formation of secondary smaller particles, as in the case of samples containing VBA-6. This

proves that the macromonomer length has a strong influence on the formation of the microgel

during the synthesis. The microgel size can be tuned better with method A while the systems,

synthesized by method B, all have a hydrodynamic radius between roughly 100 and 200 nm.

Nevertheless, it is possible to incorporate more glycidol into the colloidal network, than with

the batch method. In contrast to the microgels, synthesized with the batch method, even at very

high concentrations of the macromonomer, there is no formation of secondary smaller particles.

Figure 3.26 shows a 1H-NMR spectrum of a microgel synthesized with method B.

Figure 3.26. 1H-NMR spectrum of PVCL microgels with 3 mol% VBA-12, synthesized with

method B.

1 10 100 1.000rH / nm

pure PVCL

MG-12-0.5-B

MG-12-1.0-B

MG-12-1.5-B

MG-12-2.0-B

MG-12-3.0-B

1 10 100 1.000rH / nm

pure PVCL

MG-50-0.25-B

MG-50-0.35-B

MG-50-0.5-B

MG-50-0.75-B

MG-50-1.0-B

MG-50-1.25-B

ppm (t1)

1.02.03.04.0

4.4

52

3.9

45

3.5

36

3.5

27

3.3

02

2.9

25

2.1

37

1.9

65

1.4

21

1.4

17

1.0

0

1.9

7

1.7

1

2.1

1

7.8

7

49

Similar to the microgels from method A, the macromonomer was incorporated into the

microgel. Table 3.15 lists the theoretical and the experimentally found values of incorporated

glycidol.


macromonomer within the microgels prepared. Synthesis B.


mol%

Amountfound /

mol%

MG-12-0.5-B 0.5 0.6

MG-12-1.0-B 1.0 0.9

MG-12-1.5-B 1.5 1.65

MG-12-2.0-B 2.0 2.26

MG-12-3.0-B 3.0 3.13

MG-50-0.25-B 0.25 0.26

MG-50-0.35-B 0.35 0.30

MG-50-0.5-B 0.5 0.42

MG-50-1.0-B 1.0 0.73

MG-50-1.25-B 1.25 0.95

The theoretical and the real amounts for both systems don´t differ much from each other. The

incorporation of the macromonomer is as successful as with method A.

The temperature sensitive behavior was also analyzed and is shown in figure 3.27 for samples

MG-12 and MG-50.

50

Figure 3.27. Temperature sensitivity of samples copolymerized with VBA-12 (left) and VBA-

50 (right).

All microgels show a temperature sensitive behavior. While microgels, synthesized with

method A show a decrease in the swelling degree with an increase of the macromonomer

amount, this is not the case for microgels synthesized with method B. Here, the swelling degree

stays nearly constant for all samples. In microgels synthesized with method A, the density of

the core increases which leads to a loss in the swelling degree. But in method B the microgels

are all equally crosslinked, so the swelling remains constant. It was assumed, that the change in

the swelling degree is partly due to the influence of the head group, as this retards the reaction

and leads to a denser core and a shell which is more loosely crosslinked. The synthesis with

method B supports this theory, as the microgels are now evenly crosslinked and the temperature

sensitivity is constant, regardless of the macromonomer amount.

The colloidal stability of the microgels could not be determined using the Lumifuge approach

since the resulting dispersions were too transparent. But it can be assumed, that the colloidal

stability is better than the one for pure PVCL microgels.

To analyze their morphology, TEM measurements were done. However, they show a very bad

contrast and can hardly be analyzed. So the measurements had to be done at the SU 9000 in

TEM mode. The results are shown in figure 3.28.

0

20

40

60

80

100

120

140

160

180

200

15 25 35 45 55

rH

/ n

m

T / °C

MG-12-0.5-B

MG-12-1.0-B

VBA-12-2.0-B

MG-12-3.0-B

0

20

40

60

80

100

120

140

160

180

200

15 25 35 45 55

rH

/ n

m

T / °C

MG-50-0.25-B MG-50-0.35-B

MG-50-0.5-B MG-50-0.75-B

MG-50-1.0-B MG-50-1.25-B

51

Figure 3.28. SU 9000 TEM images of sample MG-12-2.0-A (left) and MG-12-2.0-B (right).

The microgels, synthesized with method A, are clearly visible on the grid, while the ones

synthesized with method B are harder to identify. The microgels of method A have a dense

core, because the crosslinker is concentrated there. This increases their contrast. In method B it

is evenly distributed throughout the microgel so the overall density is lower, which leads to a

decline in the contrast. It is noticeable that the A microgels show a high dispersity while the B

microgels are comparable in size.

To summarize, two different methods were established to synthesize PVCL microgels with

oligoglycidol macromonomers as comonomer. Using method A, their size can be tuned,

dependent of the amount and number of repeating units of the macromonomer. The amount of

comonomer, which can be incorporated is limited. By using method B more oligoglycidol can

be introduced into the microgel, but their size cannot be controlled anymore. Furthermore

method B only works with oligoglycidol macromonomers, which have a chain that is longer

than six repeating units.

Influence of the Macromonomer Head Group

It has been shown, that vinyl benzyl alcohol, if used as a head group in the macromonomer has

a strong influence on the speed of the reaction and the size of the formed microgels. As a

comparison, a macromonomer containing hydroxyethyl methacryl amide as a head group and

12 repeating units of glycidol was synthesized and used as a comonomer in the microgel

synthesis. Figure 3.29 shows the macromonomer used.

52

Figure 3.29. The macromonomer HAM-12.

The name of the macromonomer is HAM-12. It was used as comonomer in a microgel synthesis

with VCL. 2 mol% and 4 mol% of HAM-12 were added to the synthesis. The used synthesis

method is method A. Figure 3.30 shows the heat flow for both reactions.

Figure 3.30. Heat flow of PVCL microgel syntheses, copolymerized with HAM-12 and VBA-

12 for comparison. The key describes the type and amount of macromonomer which was used

as a comonomer.

It is noticeable, that different amounts of HAM-12 show no influence of the rate of

polymerization. Even at high amounts of comonomer the reaction starts immediately after the

addition of the initiator. In comparison, if 2 mol% of VBA-12 are added the reaction starts much

later. This confirms the above stated theory that the vinyl benzyl alcohol group is responsible

for the retardation of the polymerization process.

The composition of the microgels was analyzed via 1H-NMR spectroscopy. The spectra are

shown in figure 3.31.

0

1

2

3

4

5

6

0 500 1000 1500

Hea

t F

low

/ W

t / sec

2 mol% HAM-12

4 mol% HAM-12

2 mol% VBA-12

53

Figure 3.31. 1H-NMR spectra of PVCL microgels, modified with 2 mol% (top) and 4 mol%

bottom) HAM-12.

The signals at a chemical shift of ca. 1.40 ppm, 2.0 ppm, 2.9 ppm and 3.9 ppm all can be

assigned to the N-vinylcaprolactam. The signal at 3.28 to 3.38 ppm corresponds to the

oligoglycidol chain. By comparing the intensity of the oligoglycidol signal with the signal at

3.9 ppm, it is possible to calculate the incorporated amount of the macromonomer. Even if high

amounts of HAM-12 are used in the microgel synthesis, only a fraction is actually incorporated

into the microgel. Table 3.16 lists the theoretical and the actual values for the glycidol content.


macromonomer within the microgels prepared. Used macromonomer: HAM-12. Synthesis A.


mol%

Amountfound /

mol%

HAM-12-2.0-A 2 0.6

HAM-12-4.0-A 4 1.2

Only 30% of HAM-12 is incorporated into the microgel. The incorporation efficiency is much

lower, than comparable samples, synthesized with VBA-12.

ppm (t1)

1.02.03.04.0

4.4

75

3.9

83

3.3

43

2.9

58

2.1

76

2.0

08

1.4

54

1.0

0

0.3

6

1.7

5

2.0

1

8.5

0

ppm (t1)

1.02.03.04.0

4.4

24

3.9

33

3.3

59

3.2

88

2.9

25

2.1

28

1.9

56

1.4

09

1.0

0

0.7

2

1.7

2

2.0

2

8.3

4

54

In addition, table 3.17 lists the hydrodynamic radii and polydispersity indices for those samples.

Table 3.17. Hydrodynamic radius and polydispersity index for microgels, copolymerized with

HAM-12.

Sample Name Hydrodynamic radius /

nm

PDI

HAM-12-2.0-A 270.9 0.08

HAM-12-4.0-A 256.6 0.04

Even though the second sample has twice the amount of the glycidol incorporated in the

microgel, the actual size hardly changes. The amount of comonomer has no effect on the size.

HAM-12 does not influence the size of the microgel and its rate of incorporation into the

colloidal network is much lower than VBA-12. In conclusion it can be said, that hydroxyethyl

methacrylamide is not effective as a head group for the incorporation of glycidol into the PVCL-

microgels. The stabilizing effects of the macromonomer can only be achieved by using a fitting

head group. It was earlier shown, that the glycidol chain also has an effect on the size. However,

this effect occurs only in combination with the vinyl benzyl head group.

55

3.5 Summary and Outlook

In this chapter, oligoglycidol macromonomers were used as comonomers in the synthesis of

polyvinylcaprolactam microgels. Several macromonomers with different chain lengths and

different head groups were analyzed in their ability to copolymerize with VCL.

Their incorporation efficiency is highly dependent on the type of polymerizable head group.

While a hydroxyethyl methacrylamide head group shows only a very small incorporation

efficiency, the best results could be obtained with vinyl benzyl alcohol as a head group.

Calorimetric measurements show, that the usage of the comonomer leads to a retardation of the

polymerization process which influences the microgel structure.

Depending on the amount of incorporated macromonomer, the microgel size can be easily

controlled. Higher amounts lead to smaller microgel, while the dispersity stay constant. Smaller

microgels also show a higher colloidal stability. This is likely because of the steric stabilization

which is caused by the oligoglycidol chains. During the polymerization, the precursor particles

are getting stabilized by the macromonomers. This partly prevents the aggregation process

during the synthesis and leads to more particles which are smaller. At the same time, the

temperature sensitivity of the microgels decreases.

If too much oligoglycidol is used in method A, the microgels become very small (rH < 50 nm)

and the dispersity increasers. Therefore, another synthesis method was tested, where the

crosslinker was gradually added during the synthesis (method B). The optimal time for adding

the crosslinker was determined with the help of calorimetric measurements. These microgels

show a comparable hydrodynamic radius which is not dependent on the amount of

macromonomer used, but on the length of the oligoglycidol chain. The temperature sensitivity

stays constant regardless of the macromonomer amount, because microgels of different samples

are similarly crosslinked.

According to NMR studies, the oligoglycidol is located in the microgel shell. This result offers

the possibility for further functionalization of the OH-groups and introduction of functionalities

for new applications. This is shown in chapter 2.

56

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61

3.7 Appendix

Figure 3.32. Calorimetric measurements of PVCL microgels, copolymerized with VBA-12

and VBA-50.

Figure 3.33. Turbidity of the solution during the microgel synthesis as a function of time.

Samples: MG-12-y-A (left) and MG-50-y-A (right).

0

1

2

3

4

5

6

0 500 1000 1500

Hea

t F

low

/ W

t / sec

pure PVCL MG-12-0.5-A

MG-12-0.75-A MG-12-1.0-A

MG-12-1.5-A MG-12-2.0-A

MG-12-3.0-A

0

1

2

3

4

5

6

0 200 400 600 800 1000 1200

Hea

t F

low

/ W

t / sec

pure PVCL

MG-50-0.25-A

MG-50-0.35-A

MG-50-0.50-A

MG-50-0.75-A

MG-50-1.0-A

MG-50-1.25-A

0

5

10

15

20

25

30

0 1000 2000 3000

Tu

rb

idit

y /

%

t / sec

pure PVCLMG-12-0.5-AMG-12-1.0-AMG-12-1.5-A

0

5

10

15

20

25

30

0 500 1000 1500

Tu

rb

idit

y /

%

t / sec

pure PVCLMG-50-0.25-AMG-50-0.5-AMG-50-1.0-A

62

Table 3.17. Amounts of macromonomer used in the microgel synthesis versus the actual

amount in the microgels.

Sample Amountcalc /

mol%

Amountfound /

mol%

MG-12-0.5-A 0.5 0.72

MG-12-0.75-A 0.75 0.85

MG-12-1.0-A 1.0 1.07

MG-12-1.5-A 1.5 1.67

MG-12-2.0-A 2.0 2.23

MG-50-0.25-A

0.25

0.29

MG-50-0.35-A 0.35 0.36

MG-50-0.50-A 0.50 0.58

MG-50-0.75-A 0.75 0.76

MG-50-1.0-A 1.0 2.06

MG-50-1.25-A 1.25 1.17

63

4. Functionalization of PVCL/Oligoglycidol Microgels


Microgels can have several applications as already mentioned in chapter 1. In order to be

tailored to specific applications different functional groups must be introduced into their

structure.

PNIPAAM microgels could be modified by hydrolysis of the amide side groups to produce

carboxy groups. Or they can be modified by partial methylation resulting in a less hydrophilic

building block. [1, 2] The so-called Hoffmann rearrangement was used by Shiroya to

functionalize the NIPAAM polymer with primary amine groups. [3] With this, DNA can be

grafted onto the microgel shell. Terminal isocyanate groups of the DNA react with amino

groups incorporated into the shell. [4]

Richtering et al. used a layer-by-layer technique to deposit different layers of polyelectrolytes

on the microgel surface which lead to a change in their properties. [5]

Since NIPAAM and VCL give only limited options for functionalization it is possible to use

comonomers in the synthesis that can be modified later. A PNIPAAM/ poly (N-vinyl-

formamide) microgel was synthesized by Pelton where the formamide component can be

further functionalized to give amine groups, which are located in the microgel shell. [6] Glycidyl

methacrylate (GMA) can be used as a comonomer since the epoxy group can be easily

functionalized. It can be used to bind proteins to the microgel, to graft polymers onto it or to

functionalize the particle with amine groups. [7-9]

As already mentioned in chapter 1, poly (ethylene glycol) and polyglycidol are building blocks

often used in biomedical applications. Since they show a good biocompatibility, they can be

used as coating materials to prevent unspecified protein absorption. Especially the polyglycidol

building block can be used for additional applications, mainly by modifying the OH groups.

For example star-shaped poly (ethylene glycol) can be used as coating material and

functionalized with isocyanate groups. These groups readily hydrolyze in water to form amino

groups and the coating now shows a resistance against unspecified protein adsorption. The layer

can now be further modified with RGD peptides and seeded cells can now grow on the

functionalized surface, while there is no growth on the unfunctionalized one. [10]

In addition, the OH group can be further functionalized to get a cyanide group, which can be

reduced with a Raney-cobalt catalyst to produce amine groups. This is important for the

64

biological application, as ethanolamine is an important head group for phospholipids. There are

many more biological components which contain amino alcohols, consequently the polymer

may play a biomimetic role. [11]

It has been reported by Groll et al., that polyglycidol could be successfully crosslinked with

disulfide groups, to form degradable nanogels. The degradation results from the conversion of

the disulfide bond and formation of thiol groups. Cytotoxicity experiments show a low toxicity,

which makes these nanogels interesting systems for drug delivery. [12]

Star shaped polyglycidol was functionalized with vinyl sulfonate groups on their end by

Haamann et al. These groups are selective in the reaction with amine groups, so that peptides

can be bound to the polymer. Potentially, synthetic protein/ peptide-conjugates can be prepared.

[13]

65

4.2 Aim

In this chapter, the incorporation of several functional groups into microgels prepared by

precipitation polymerization of N-vinylcaprolactam and oligoglycidol macromonomers was

studied. There are already several publications on the postmodification of microgels. But there

are several drawbacks. Postmodification of PNIPAAM microgels leads mainly to amide

derivatives. [3] Other functionalities are also available but the chosen reaction conditions are

very harsh or lead only to low yields. [3, 14] The incorporation of comonomers seems to be a

suitable alternative but there are some drawbacks here too. While glycidyl methacrylate can be

modified with several functional groups due to its epoxy group, it has a higher polymerization

rate than VCL or NIPAAM. If it is copolymerized with one of the two monomers, a particle

forms, where the GMA is located in the core. [15] Thus a surface functionalization is not possible.

In addition GMA is a toxic monomer and not suitable for the use in medical or biological

applications.

The oligoglycidol macromonomer is biocompatible and it has been shown in chapter 1 that the

OH groups are located on the microgel surface. Therefore, it should be easy to modify the

microgels shell with a multitude of different functional groups. Because of its porosity it is

entirely possible that hydrophobic groups that are grafted on the microgel surface can retreat

into its core. The hydrophilic comonomer should act as some kind of spacer and keep the group

on the surface.

Different approaches were tested, to incorporate allyl-, vinyl sulfonate- and thiol groups into

the microgel structure (Scheme 4.2.1).

Scheme 4.1. Functionalization of polyglycidol with allyl-, vinyl sulfonate-, and thiol groups.

66

The functionalization with allyl- and thiol groups on microgels has already been attempted to

synthesize hydrogels consisting of crosslinked microgels. [16] The functionalization with thiol

groups has also been researched in an effort to synthesize colloids which can be bound to hair.

[17] The aim was to synthesize microgels with a defined amount of specific functional groups

on the surface and to determine if the functionalization has an effect on the colloidal properties.

67


The microgels used are presented in chapter 3. PVCL based microgels are copolymerized with

different oligoglycidol macromonomers with vinyl benzyl alcohol as a head group. The

synthesized microgel samples are further referred to as MG-x-y-A or MG-x-y-B. X stands for

the number of repeating units in the macromonomer whereas y stands for the amount of

macromonomer used in mol% in relation to the used molar amount of VCL. A means that the

microgel was synthesized by batch synthesis. B means that the microgel was synthesized by the

continuous method which means that the crosslinker was added over a certain time after the

addition of the initiator to the reaction mixture.

Functionalization of MG-6-2.5-A with allyl groups

MG-6-2.5-A (300 mg, 0.33mmol OH groups) is dispersed in DMF (25 mL). KOtBu (1M in

THF) is slowly added and the dispersion is stirred for 2 hours at room temperature. After

removing THF by applying vacuum, allyl bromide and a catalytic amount of potassium iodide

are added and the dispersion is stirred over night at room temperature. The microgel is cleaned

via dialysis and the product is obtained as a white powder after freeze drying.

The following table lists the different amounts of reagents, that were used and the yield.

68

Table 4.1. Amount of educts used in the functionalization of microgels with vinyl groups.

Sample

KOtBu / µL ( eq) Allyl bromide /

mg; mmol ( eq)

Gravimetric yield /

%

V-1 261.52 (0.8) 31.64; 0.26 (0.8) 95

V-2 261.52 (0.8) 47.46; 0.39 (1.2) 98

V-3 196.14 (0.6) 23.73; 0.20 (0.6) 96

V-4 196.14 (0.6) 35.59; 0.29 (0.9) 94

V-5 326.90 (1.0) 59.32; 0.49 (1.5) 57

V-6 326.90 (1.0) 39.55; 0.33 (1.0) 86

V-7 392.28 (1.2) 47.46; 0.39 (1.2) 87

V-8 392.28 (1.2) 59.32; 0.49 (1.5) 85

V-9 326.90 (1.0) 79.10; 0.65 (2.0) 96

V-10 653.80 (2.0) 79.10; 0.65 (2.0) 86

The equivalents (eq) of the educts in the table are given with respect to the molar amount of

hydroxyl groups in 300 mg of the microgel (MG-6-2.5-A).

1H-NMR (D2O):

δ (ppm) = 1.00-2.20 (m, 320H, H-2, H-5), 2.20-2.80 (m, 80H, H-1), 2.80-3.50 (m, 80H, H-3),

3.50-3.80 (m, 30H, H-6, H-7, H-10-13), 3.96 (m, varying amounts, H-14), 4.00-4.58 (m, 40H,

H-4), 7.31 (m, 4H, H8, H9), 5.16 (m, varying amounts, H-16), 5.84 (m, varying amounts, H-

15).

69

Functionalization of MG-12-3.0-B with vinyl sulfonate groups

MG-12-3.0-B (300 mg, 0.67 mmol OH groups) is dispersed in DCM (20 mL) overnight.

Triethylamine (TEA) is slowly added and the dispersion is cooled to 0°C with an ice bath. Then

2-chloroethane sulfonyl chloride (CSC) is slowly added. The dispersion is stirred at 0°C for 20

more minutes and afterwards stirred for two hours at room temperature. The reaction mixture

is dialyzed against ethanol for half a day and afterwards dialyzed against distilled water. The

product is obtained as a white powder after freeze drying.

The following table lists the different amounts of reagents, that were used and the yield.

Table 4.2. Amount of educts used in the functionalization of microgels with vinyl sulfonate

groups.

Sample TEA /

mg; mmol (eq)

CSC /

mg; mmol (eq)

Gravimetric yield /

%

VS-1 270.77; 2.68 (4) 216.59; 1.33 (2) 80

VS-2 270.77; 2.68 (4) 433.18; 2.66 (4) 91

VS-3 541.54; 5.35 (8) 433.18; 2.66 (4) 68

VS-4 270.77; 2.68 (4) 866.36; 5.31 (8) 17

VS-5* 270.77; 2.68 (4) 216.59; 1.33 (2) 90

VS-6** 270.77; 2.68 (4) 216.59; 1.33 (2) 93

* The reaction conditions were similar to VS-1 but in addition a surfactant was used to try to stabilize the product during

dispersion.

** The reaction conditions were similar to VS-1 but the reaction time was increased to 24 hours.

The equivalents (eq) of the educts in the table are given with respect to the molar amount of

hydroxyl groups in 300 mg of the microgel (MG-12-3.0-B).

70

1H-NMR (D2O):

δ (ppm) = 1.00-2.20 (m, 267H, H-2, H-5), 2.20-2.80 (m, 67H, H-1), 2.80-3.50 (m, 67H, H-3),

3.50-3.80 (m, 33H, H-6, H-7, H-10-13), 3.96 (m, 60H, H-14), 4.00-4.58 (m, 33H, H-4), 7.31

(m, 4H, H8, H9), 6.35 (m, varying amounts, H-15), 6.76 (m, varying amounts, H-14).

Functionalization of MG-12-2.5-B with Thiol Groups

MG-12-3.5-B (300 mg; 0.57 mmol OH groups) is dispersed in DMF (5 mL). Dicyclo-

hexylcarbodiimide (DCC) and dimethylaminopyridine are added and the whole dispersion is

cooled down in an ice bath to 0°C. 3,3´-dithiopropionic acid (DTPA) is dissolved in DMF (2

mL) and slowly added to the reaction. The mixture is stirred overnight at room temperature.

During this time, the dispersion turns turbid and slightly yellow. Afterwards PBS buffer

solution (pH = 7.4, 10 mL) is added to the reaction mixture and dithiothreitol is slowly added.

The reaction is stirred at room temperature for 2 hours. For purification, the mixture is filled in

a dialysis tube under an inert gas atmosphere and dialyzed for one day against HCl solution

with a pH between 3 and 4. The mixture is further dialyzed against water for 2 more days.

Afterwards, the mixture is further purified by centrifugation (1000 rpm, 3 minutes). The product

is obtained as white to slightly yellow powder.

The following table lists the different amounts of reagents that were use, and the corresponding

yield.

71

Table 4.3. Amount of educts used in the functionalization of microgels with thiol groups.

Sample DCC /

mg (mmol)

DMAP /

mg (mmol)

DTPA/

mg (mmol)

DTT /

mg (mmol)

Gravimetric

yield / %

T-1 63.00

(0.30)

37.00

(0.30)

29.00

(0.14)

32.00

(0.20) 47

T-2 125.00

(0.61)

74.00

(0.61)

58.00

(0.28)

63.00

(0.61) 38

T-3 187.00

(0.91)

111.00

(0.91)

87.00

(0.41)

96.00

(0.61) 26

T-4 250.00

(1.21)

148.00

(1.21)

116.00

(0.55)

128.00

(0.82) 48

1H-NMR (D2O):

δ (ppm) = 1.00-2.20 (m, 8H, H-2, H-5), 2.20-2.80 (m, 2H, H-1), 2.80-3.50 (m, 2H, H-3), 3.50-


72


When VCL is copolymerized with oligoglycidol macromonomers to form a microgel, it has

been shown that the OH groups of the glycidol repeating unit are mainly located on the microgel

surface. This makes them desirable to modify them with new functional groups. They would

also be located on the surface and would be easily accessible. The introduction of different

groups on the nanogel surface is discussed here.

Functionalization of Microgels with allyl groups

By using allyl bromide in a Williamson ether synthesis, it is possible to functionalize the

microgels with allyl groups. Scheme 4.4.1.1 shows the reaction scheme.

Scheme 4.2. Mechanism of a Williamson ether synthesis using an oligoglycidol building block

and allyl bromide.

By using potassium tert-butoxide as a proton acceptor, the negative charge shifts to the oxygen

atom at the microgel, which can now substitute the bromide within the allyl bromide. A catalytic

amount of potassium iodide is used, which replaces the bromide, so that the nucleophilic

substitution proceeds easier, analogous to a Finkelstein reaction. The reaction is performed in

dimethylformamide, because an aprotic solvent is needed. As a microgel, MG-6-2.5-A was

chosen in the functionalization reaction. The analysis of the product was done via 1H-NMR

spectroscopy. Figure 4.1 shows the spectrum for one product.

73

Figure 4.1. 1H-NMR spectrum of MG-6-2.5-A before (a) and after functionalization with allyl

bromide (b). Used amounts of KOtBu: 1.0 eq. Used amounts of allyl bromide: 1.5 eq (Sample

V-5).

The signals at ca. 1.69, 2.40, 3.19 and 4.20 ppm correspond to the protons of the VCL repeating

units while the signal at 4.7 ppm can be assigned to the solvent water. The signal at ca. 3.62

ppm is caused by the protons of the glycidol repeating chain. The signals at 3.96, 5.16 and 5.84

ppm do not appear in the spectrum for an unmodified microgel. These are caused by the allyl

groups, which are now incorporated into the microgel. The question now arises, if the allyl

groups are covalently bound to the microgel, or if the allyl bromide is just contained inside the

porous structure. The first clue is the broadness of the peak signal of the allyl groups. The

covalent bonding to the colloidal network leads to a loss of mobility for the allyl group, which

leads to a broadening of the NMR signals, which is the case here.

Nevertheless an experiment was done, where allyl bromide was mixed with a PVCL-

oligoglycidol microgel without adding KOtBu or KI. The mixture was dialyzed for a few days.

The hypothesis is, that if the allyl bromide is not covalently bound to the microgel, then it will

be washed out of the mixture. Analysis with 1H-NMR-spectroscopy shows, that there is no trace

of the allyl groups left. They could be washed out without a problem. This leads to the

conclusion that after the Williamson ether synthesis, the allyl groups are covalently bound to

ppm (t1)

1.02.03.04.05.06.0

4.7

00

4.2

00

3.7

84

3.7

80

3.6

29

3.5

46

3.1

85

2.4

00

2.2

27

1.6

98

1.0

0

0.7

5

1.6

7

2.0

8

6.4

6

ppm (t1)

1.02.03.04.05.06.0

5.8

45

5.1

62

4.7

00

4.2

01

3.9

61

3.6

23

3.5

40

3.1

94

2.4

02

2.2

27

1.6

96

1.0

0

0.6

3

1.5

6

1.8

8

5.8

0

0.1

3

0.0

7

0.0

4

a

b

74

the microgel. Since the oligoglycidol is located on the microgel surface, it is safe to say, that

the allyl groups are also located on the surface, which means they are more accessible to further

reactions.

Usually, it is possible, to calculate the degree of functionalization by comparing the signal

intensity of the allyl groups with the intensity of the glycidol groups. However, since the allyl

signals are very weak, it is very difficult to obtain a clear result. Therefore, a different

quantification method was employed. The amount of allyl groups was determined by

iodometric titration. In this redox titration, iodine monochloride is added to a small amount of

the functionalized microgel. In an addition reaction, the iodochloride adds to the vinyl groups,

as shown in scheme 4.3.

Scheme 4.3. Addition mechanism of iodine monochloride to a vinyl group.

The excess of ICl is now mixed with NaI, which forms elemental iodine. The iodine is then

titrated with sodium thiosulfate. Scheme 4.4 shows the reaction equation.

Scheme 4.4. Reaction of ICl with NaI and sodium thiosulfate.

After the addition of sodium iodide, the solution becomes yellow/orange. The color disappears

after enough sodium thiosulfate was added, to consume the whole amount of iodine. In addition

to the titration of the functionalized samples, the unfunctionalized microgel was also titrated as

a reference. Table 4.4 now lists the conversion of the OH groups along with the size and

dispersity of the microgels.

75

Table 4.4. List of different samples and conversion of OH groups.

Sample

Amount

KOtBu /

eq*

Amount

Allylbromide /

eq*

Conversion of

OH groups / % rH / nm PDI

0 0 0 / 57.85 0.18

V-1 0.8 0.8 21 72.64 0.29

V-2 0.8 1.2 36 77.67 0.32

V-3 0.6 0.6 0 80.78 0.33

V-4 0.6 0.9 21 75.58 0.31

V-5 1 1.5 37 78.04 0.33

V-6 1 1 22 74.44 0.29

V-7 1.2 1.2 38 84.90 0.59

V-8 1.2 1.5 39 84.90 0.69

V-9 1 2 43 82.70 0.79

V-10 2 2 64 80.10 0.68

*The equivalents (eq) of the educts in the table are given with respect to the molar amount of hydroxyl groups in the microgel

(MG-6-2.5-A).

According to the results, both KOtBu and allylbromide have an influence in the efficiency of

functionalization. In general, it seems that with increasing amount of both educts, the

conversion increases. An amount of 0.6 equivalents for both chemicals shows a conversion that

is too small to be detected with 1H-NMR spectroscopy or to be quantified by iodometric

titration. It can be concluded, that it is possible to control the efficiency of functionalization

(conversion of OH groups) by the ratio of reagents to substrate used.

In addition, the hydrodynamic radii and the PDI were also measured. As can be observed in

table 4.4 every sample shows an increase of the radius by 15-25 nm. The PDI also increases.

Especially if more than 1 equivalent of allyl bromide and KOtBu are used, there is a sharp

increase in the dispersity. This suggests, that some form of aggregation takes place, which

becomes stronger with increasing conversion of OH-groups on the surface of the microgels.

With the disappearance of the OH-groups the steric protection disappears and agglomeration,

induced by the hydrophobic groups is favored.

76

In figure 4.2 the size of a microgel sample was measured at different temperatures to check if

the microgels still show some temperature sensitivity. The sample concentration was

comparable in both experiments.

Figure 4.2. Temperature sensitivity of a microgel before and after the functionalization with

allyl groups.

After the functionalization the microgel shows a slightly changed temperature sensitivity

compared to the original one. Since the sensitivity of the original microgels is very low anyway,

the changes are negligible. The idea is, that only the microgel surface is modified with the allyl

group, so the VCL core remains unchanged in regard to the temperature sensitivity. But there

is now a slight aggregation visible at 33°C which suggests that the steric protection of the

oligoglycidol groups is diminished because of the functionalization.

In conclusion, the conversion of OH groups to allyl groups is successful, although the dispersity

of the microgels can be improved.

0

20

40

60

80

100

120

140

15 25 35 45 55

rH

/ n

m

T / °C

MG-6-2.5-A

V-7

77

Functionalization of Microgels with Vinyl Sulfonate Groups

The functionalization with vinyl sulfonate groups is done with triethylamine and 2-chloro-

ethyl-sulfonyl chloride, as shown in scheme 4.5.

Scheme 4.5. Functionalization of hydroxyl groups with vinyl sulfonate groups. [20]

An elimination reaction takes place, where hydrogen chloride is cleaved from the group and the

product is formed. Triethylamine is used to neutralize the formed hydrogen chloride.

Afterwards a nucleophilic substitution takes place which leads to a sulfonate ester. The alcohol

function reacts with the intermediate to form the vinyl sulfonate group. The triethylamine is

used again to neutralize the formed hydrogen chloride. [20] The analysis of the reaction product

was done via 1H-NMR spectroscopy (figure 4.3).

Figure 4.3. 1H-NMR spectrum of MG-12-3.0-B functionalized with vinyl sulfonate groups.

Sample: VS-2.

As with figure 4.1, the signals below 4.00 ppm can all be assigned to the protons of the PVCL

and the oligoglycidol. At 6.35 and 6.76 ppm new signals can be found. These signals can be

assigned to the protons of the vinyl sulfonate groups. The functionalization was successful.

ppm (t1)

1.02.03.04.05.06.07.0

6.7

64

6.3

50

4.7

56

4.2

36

3.6

07

3.6

04

3.6

01

3.2

32

2.4

38

1.7

24

1.0

0

1.8

6

1.7

7

2.1

1

0.0

4

0.0

6

7.4

7

78

However, due to the weak signal intensity, a quantification is difficult and cannot be done

precisely. The size of the modified microgels was analyzed and is shown in table 4.5.

Table 4.5. Size of the microgels functionalized with vinyl sulfonate groups.

Sample Triethylamine /

eq.

2-Chloroethane

sulfonyl chloride / eq. rH / nm PDI

Unmodified

microgel 0 0 149.0 0.14

VS-1 4 2 135.2 0.23

VS-2 4 4 153.4 0.35

VS-3 8 4 / /

VS-4 4 8 / /

VS-5 4 2 180.4 0.43

VS-6 4 2 110.2 0.32

The results indicate, that the size of the microgels does not change much. The highest size

difference to the unmodified sample is around 30 nm. But the dispersity is much higher. Also,

after the reaction and the cleaning process, the microgel is much harder to redisperse in water

than before. The samples VS-3 and VS-4 were not redispersible in water so the hydrodynamic

radius could not be determined.

Since vinyl sulfonate groups tend to react with OH groups under optimal conditions, interchain

reactions of different microgels leads to particle coupling. In addition, the number of hydroxyl

groups per particle is diminished which could lead to a decrease in the hydrophilicity of the

colloidal network and consequently to agglomeration by hydrophobic interaction. The

microgels aggregate during the drying process. When they are redispersed they are still

aggregated which in turn leads to the higher dispersity. To stabilize the colloidal network

sample VS-5 was synthesized. During the dialysis a surfactant was added to stabilize the

dispersion. But according to the light scattering data there is no change in the dispersity. The

effect of the reaction time was also analyzed by increasing the time to 24 h (sample VS-6). An

79

effect on the functionalization could not be observed, since the 1H-NMR spectrum of the sample

did not show a higher sulfonate signal intensity than sample VS-1. But the gravimetric yield

was slightly higher.

The temperature sensitivity was analyzed for a selected sample and is shown in figure 4.4.

Figure 4.4. Temperature sensitivity of microgel MG-12-3.0-B before and after the

functionalization with vinyl sulfonate groups.

The functionalized microgels are larger, however the ratio of rH of swollen and collapsed

microgels is similar to the non-functionalized ones. The temperature sensitivity was not

influenced by the modification with vinyl sulfonate groups. Since the functionalization happens

at the microgel surface, it is reasonable to assume, that the temperature sensitivity does not

change very much because it is mainly influenced by the PVCL part.

0

20

40

60

80

100

120

140

160

180

200

15 25 35 45 55

rH

/ n

m

T / °C

MG-12-3.0-B

VS-2

80

Functionalization with thiol groups

It is possible, to functionalize the microgels with thiol groups. Scheme 4.6 shows the reaction.

Scheme 4.6. Thiol functionalization of polyglycidol.

3,3´-dithiopropionic acid (DTPA) and the hydroxyl groups of the glycidol react in a Steglich

esterification and form an ester bond. Afterwards, the disulfide bond is cleaved via reduction to

thiol groups with dithiothreitol. The resulting samples were analyzed via Raman spectroscopy

(figure 4.5.).

Figure 4.5. Raman spectrum of thiol modified microgels.

The signal at 2570 cm-1 corresponds to the thiol groups, which are incorporated into the

microgel. With a higher degree of functionalization, the signal becomes stronger. In the non-

modified microgel this signal is absent. In addition, there is also a signal at 1750 cm-1 which is

caused by the ester group, which is formed during the Steglich esterification. Because of the

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

30080013001800230028003300

Ra

ma

n i

nte

nsi

ty

Wave number / cm-1

MG-12-2.5-BT-1T-2T-3T-4

0

0,05

0,1

0,15

2500260027002800

Ram

an

In

ten

sity

Wave number / cm-1

2570 cm-1

1750 cm-1

81

small amount of thiol groups, which are incorporated into the microgel, a quantitative analysis

of the samples via Raman spectroscopy is not possible. To calculate the amount of thiol groups

in the microgel, the samples were analyzed by Ellmann method. To the samples, a fixed amount

of 5,5´-dithiobis (2-nitrobenzoic acid), also known as Ellmanns reagent was added. The reagent

reacts with the thiol groups of the microgel, and the disulfide bond of the reagent is cleaved.

The resulting 2-nitro-5-thiobenzoate becomes ionized in water and shows a characteristic

yellow color, which can be measured via UV/VIS spectroscopy. [18, 19] To calculate the amount

of thiol groups in the samples, a calibration curve was measured, with fixed amounts of N-

acetyl L-cysteine, which is shown in figure 4.6.

Figure 4.6. Light absorption of fixed concentrations of N-acetyl L-cystein. Wavelength: 412

nm.

The slope of the trend line is given as:

y = 11.604x

From this, the amount of thiol groups for each sample could be calculated. They are shown in

table 4.6.

0

0,2

0,4

0,6

0,8

1

1,2

1,4

0 0,02 0,04 0,06 0,08 0,1

Ab

sorp

tio

n /

a. u

.

Concentration / mmol/L

82

Table 4.6. Calculated amount of thiol groups in the synthesized samples.

Sample eq. DTPA per OH-group

used

Amount thiol groups

(calculated)

T-1 0.5 9.79%

T-2 1.0 15.00%

T-3 1.5 25.97%

T-4 2.0 26.68%

The percentage relates to the amount of hydroxyl groups which were functionalized. Even the

lowest amount of 0.5 equivalents of DTPA per OH group should ideally lead to a

functionalization rate of 100%. The actual amount of thiol groups is much smaller, than the

desired one. With more equivalents of the DTPA used, the amount of thiol groups increases.

But the amount of sample 3 is not much higher than the amount of sample 4. This suggests, that

there is an upper limit to how much hydroxyl groups can be functionalized with thiol groups.

This could be because at high concentrations of DTPA, it can´t react with the OH groups

anymore, because of a steric hindrance.

After the functionalization, the size of the microgels was analyzed and compared with the

unmodified microgel. The results are shown in table 4.7.

Table 4.7. Hydrodynamic size and dispersity of the samples, functionalized with thiol groups.

Sample rH / nm PDI

MG-12-2.5-B 149.43 0.14

T-1 260.72 0.37

T-2 181.95 0.34

T-3 121.11 0.34

T-4 199.58 0.32

There is no clear trend visible. The size fluctuates around the original size of the unmodified

microgel. But it seems, that the hydrodynamic radius increases after the modification. In every

sample, the PDI more than doubles. During the modification process, the microgels might tend

to aggregate, which leads to the higher PDI. One aggregation process is possible, when the

esterification of the DTPA takes place and OH groups from two different microgels are

involved with the reaction. This leads to an entanglement of the particles which might be

permanent.

83

The temperature sensitivity of the sample with the highest amount of thiol groups was measured

to determine if the change in the hydrophilicity, which occurs because of the modification, has

any influence on the swelling degree. They are shown in figure 4.7.

Figure 4.7. Temperature sensitivity of microgel MG-12-3.5-B before and after the

functionalization with thiol groups.

The microgels which possess the highest amount of thiol groups show a comparable

temperature sensitivity as the unmodified microgel. By comparing the radius of the collapsed

microgel at 51°C with the swollen one at 15°C, a value for the shrinking and swelling degree

can be calculated. The value for the unmodified sample is 0.54 and the one for T-4 is 0.49. The

values are very similar. This means that the functionalization does not significantly influence

the microgel properties.

0

20

40

60

80

100

120

140

160

180

200

15 25 35 45 55

rH

/ n

m

T / °C

MG-12-2.5-B

T-4

84


In conclusion, it is possible, to functionalize the microgels with several different functional

groups. The degree of functionalization can be varied in most cases. Because the OH-groups

are located on the microgel surface, the new functional groups are easily accessible for further

modifications. In addition, aside from changes in the dispersability, the microgel properties

such as the temperature sensitivity do not seem to change.

The functionalization with allyl groups follows a trend that with higher amounts of base and of

allyl bromide the number of functionalized OH-groups increases. The radius only changes

slightly for the modified microgels, but if the conversion is too high, then the dispersity sharply

increases. This is presumably because of particle aggregation as the stabilizing effect of the

dispersion decreases with conversion of the OH-groups.

Vinyl sulfonate groups could be successfully introduced into the colloidal network. The radius

and the dispersity increase slightly but if the amount of TEA and CSC is too high the microgels,

once isolated cannot be redispersed in water. Because of the low intensity of 1H-NMR signals

of the vinyl sulfonate groups formed, it was not possible to quantify these groups.

It is possible to functionalize the microgel with thiol groups. With an increasing amount of

DTPA the degree of ester formation increases up to an upper limit of 25% of functionalized OH

groups. The size of the modified samples varies highly while the dispersity increases.

The dispersity of all samples presumably also increases because the microgels are getting dried

and redispersed in different solvents several times during the reaction which can lead to

aggregation and entanglement of particles which can hardly be reversed. Since the hydroxy

groups are located on the shell, the functional groups are also located there. They can be easily

reached if they have to interact with other molecules for specific purposes.

There are several possible applications for functionalized microgels based on the properties of

the functional groups.

Thiol groups are used, to specifically bind to hair, which makes the application of microgels in

cosmetics possible. [17]

Thiol- and allyl groups react together in a click reaction by applying light of a certain

wavelength. By functionalizing microgels with those groups, hydrogels could be formed from

them. [16]

Vinyl sulfonate groups could help in the formation of collagen hydrogels. Since the microgels

usually have more than one vinyl sulfonate group per particle, they can readily react with the

amine groups of the collagen and act as crosslinkers. Based on experiments, it could be

observed, that the gelation time can be shortened.

85

In addition to the functional groups mentioned in this chapter, there are many more with which

the hydroxyl groups can be functionalized. Even enzymes and proteins could be grafted on the

microgel surface.

It is possible, to functionalize the microgels with relative ease. Not only can the OH groups be

used to introduce new groups into the microgel, they can also be used as initiators for new

polymerizations, extending from the surface.

86

4.6 Literature

[1] Hoare, T.; Pelton, R. Langmuir 2004, 20, 2123-2133.

[2] Snowden, M. J.; Marston, N. J.; Vincent, B. Colloid. Polym. Sci. 1994, 272, 1273-

1280.

[3] Shiroya, T.; Tamura, N.; Yasui, M.; Fujimoto, K.; Kawaguchi, H. Colloids and

Surfaces B-Biointerfaces 1995, 4, 267-274.

[4] Delair, T.; Meunier, F.; Elaissari, A.; Charles, M. H.; Pichot, C. Colloids Surf. A

Physiochem. Eng. Asp. 1999, 153, 341-353.

[5] Greinert, N.; Richtering, W. Colloid Polym. Sci. 2004, 282. 1146-1149.

[6] Xu, J.; Pelton, R. J. Colloid. Interf. Sci. 2004, 276, 113-117.

[7] Xu, F. J.; Cai, Q.; J.; Li, Y. L.; Kang, E. T.; Neoh, K. G. Biomacromolecules, 2005, 6,

1012-1020.

[8] Virtanen, J.; Baron, C.; Tenhu, H. Macromolecules 2000, 33, 336-341.

[9] Häntzschel, N.; Schrinner, M.; Hund, H.; Hund, R. D.; Lück, C.; Pich, A. Macromol.

Biosci. 2009, 9, 444-449.

[10] Groll, J.; Fiedler, J.; Engelhard, E.; Ameringer, T.; Tugulu, S.; Klok, H.-A.; Brenner, R.

E.; Moeller, M. J. Biomed. Mater. Res. Part A 2005, 74A, 607-617.

[11] Keul, H.; Möller, M. J. Polym. Sci. Part A: Polym. Chem. 2009, 47, 3209-3231.

[12] Groll, J.; Singh, S.; Albrecht, K.; Möller, M. J. Polym. Sci. Part A 2009, 47, 5543-

5549.

[13] Haamann, D.; Keul, H.; Klee, D.; Möller, M. Macromolecules 2010, 43, 6295-6301.

[14] Zhso, J. P.; Schlaad, H. Macromolecules 2011, 44, 5861-5864.

[15] Qui, X.; Sukhishvili, S. J. Polym. Sci. A Polym. Chem. 2006, 44, 183-191.

https://www.researchgate.net/journal/1099-0518_Journal_of_Polymer_Science_Part_A_Polymer_Chemistry

87

[16] Hoffmann, A. Diploma Thesis, Funktionalisierungen von N-vinylcaprolactam- und N-

isopropylmethacrylamid- basierten Mikrogelen zur Photovernetzung, 2013, Rheinisch-

Westfälische Technische Hochschule Aachen.

[17] Daleiden, N. J. E. Diploma Thesis, Synthese von thiolfunktionalisierten P(VCL-co-PG)

Mikrogelen, 2013, Rheinisch-Westfälische Technische Hochschule Aachen.

[18] Ellmann, G. L. Arch. Biochem. Biophys. 1959, 82, 70-77.

[19] Tsukamoto, Y.; Wakil, S. J. J. Bio. Chem. 1988, 263, 16225-16229.

[20] Whitmore, W. F.; Landau, E. F. J. Am Chem. Soc. 1946, 68, 1797-1798.

88

5. Modification of the Microgel Surface with Polymer

Brushes


The grafting of polymers onto surfaces can be used to synthesize composite materials. Those

can be used in different applications such as the immobilization of proteins or colloidal

stabilization of particles. [3, 4] Especially the modification of the particle surface has been

researched in the past.

There are two methods to modify a surface. It can be realized either by grafting-to or by grafting

from polymerization. The first method allows a better control over the grafted polymer chains.

However, because of sterical hindrance, the graft density is rather low. [5] The grafting-from

polymerization does not show this problem, as the monomers can more easily reach the active

sites.

Polymers can be grafted from different surfaces. Rühe et al. reported the formation of

polystyrene on the surface of a silica gel. The surface is covered with a monolayer of

azoinitiator, which is covalently bound to the surface and the polystyrene is synthesized by free

radical polymerization. [6] Silica particles could also be functionalized with poly (butyl acrylate)

by living free radical polymerization. [7]

It is also possible to modify the surface of organic colloidal systems like this. Zheng and Stöver

reported the grafting of polystyrene from disperse polydivinylbenzene particles. Remaining

vinyl groups on the surface were modified so that the styrene could be polymerized by atom

transfer radical polymerization (ATRP). [8] Ballauf et al. developed a colloidal system

consisting of a polystyrene core and different anionic or cationic polyelectrolyte chains grafted

onto it which could be used as nanoreactors for the synthesis of metal nanoparticles. [9, 10] Poly

(ethylene glycol methacrylate) (PEGMA) could be grafted from polystyrene particles that have

been functionalized with a photoinitiator. The PEGMA was synthesized by

photopolymerization and the resulting particles have been used as nanoreactors for the

generation of stable Ag nanoparticles. [11]

Most particles show a slight increase in their size which comes from the polymer brushes on

the surface while some systems show changed properties in different solvents. Depending on

Excerpts of this chapter have already been published elsewhere. [1, 2]

89

the grafted polymer and the solvent, aggregation of the particles can be promoted by adding a

poor solvent. [7-9]

The different systems were mostly functionalized by modifying the surface with a specific

reagent or initiator to induce polymerization. It could be shown in chapter 3, that oligoglycidol

macromonomers could be copolymerized with VCL to form microgels and that they are located

on the microgel surface. The OH groups can either be directly used or functionalized so that the

groups on the shell can be utilized as macroinitiators for further polymerizations. There are

several techniques to graft polymers onto the polyglycidol backbone. This chapter focuses on

redox polymerization and single-electron-transfer living radical polymerization (SET-LRP).

Redox Polymerization

Redox polymerization means the involvement of metallic oxidation agents in combination with

reducing agents like alcohols or aldehydes to synthesize block copolymers. These oxidation

agents can be Mn(II)-, V(V)-, Cr(II)-, Co(III)-, Fe(III)- or Ce(IV) salts. [12-15]

Especially cerium nitrates or sulfates can form effective redox systems in the presence of

organic reducing agents, like alcohols, aldehydes, amines or thiols. Ceric salts show a high

reactivity in aqueous media and have been used in the polymerization of vinylic monomers. [16-

18] The polymerization can be performed at room temperature, which minimizes potential side

reactions and makes it especially attractive for the polymerization of thermally sensitive

monomers. This reaction is also desirable to synthesize graft polymers. If for example

polyethylene glycol or polyglycidol are used, the radical can only be formed at the already

existing backbone. The radical is generated at the C-atom substituted with the OH group. This

is illustrated in scheme 5.1. [16]

Scheme 5.1. Redox polymerization with Ce (IV) salts in the presence of a primary or secondary

alcohol groups. [16]

The aqueous Ce (IV) ion and the alcohol can form an intermediate coordination complex with

each other. The reduction of the cerium ion happens in a single-electron-transfer process and a

90

radical is formed next to the hydroxyl group. In the presence of vinyl or acrylate groups, a

polymerization is initiated and the propagation follows the mechanism of a typical radical

polymerization. This can be done at room temperature. Titration of the Ce(IV) ions has shown,

that most of the ions are consumed in the first 5 minutes of the reaction. The reaction rate is not

decided by formation of the intermediate complex, but by the single-electron transfer happening

afterwards. [17] If the polymerization is carried out in water, the cerium ion can form a complex

with it, which leads to a form where the cerium ion is less reactive regarding the radical

formation. This complexation is illustrated in scheme 5.2. [19]

Scheme 5.2. Oxidation mechanism of Ce4+ in water. [19]

This has adverse effects on the polymerization reaction. The (Ce-O-Ce)6+ complex is unable to

form the intermediate complex with the reducing agent. To counter this, the reaction is carried

out in acidic medium, to shift the equilibrium to the Ce4+. A too high acid concentration also

has adverse effects on the polymerization, so the pH has to be chosen carefully. It is not only

dependent on the amount of acid in the medium. The nature of the acid is equally important for

the reaction rate. The rate of polymerization is highest with HClO4, lower with HNO3 and

lowest with H2SO4. This is because the oxidation potential for the Ce4+/Ce3+ is highest with

HClO4. [20]

Single Electron Transfer Living Radical Polymerization

In addition to the redox polymerization with metallic oxidation agents, it is possible to use a

single-electron-transfer living radical polymerization (SET-LRP) to graft polymers onto a

surface. Like a RAFT- or ATRP-reaction, SET-LRP is a controlled polymerization, in which

the presence of an active and a dormant species is used. [21] The active species is a radical and

the dormant species is commonly an alkyl halide species, which does not participate in the

polymerization. Contrary to a radical free polymerization, the course of the polymerization is

tightly controlled. Because the equilibrium between active and dormant species is shifted

towards the dormant species, there is always only a small amount of radicals active in the

reaction, which leads to a drastic reduction of side reactions or chain terminations. In such

reactions, metals with low oxidation states are used as activators or electron transfer agents,

such as iron, osmium, ruthenium or molybdenium compounds. In a SET-LRP copper is used as

91

the electron transfer agent. An overview over the polymerization mechanism has been reported

by Percec in 2006 and is shown in scheme 5.3. [22]

Scheme 5.3. Schematic description of the activation/deactivation process of the radical in a

SET-LRP. [22]

A copper (0) species is used which acts as an electron donor agent. The electron is transferred

to the dormant species and an intermediate radical anion is formed. It decomposes into a Cu(I)

complex and the active species which starts the polymerization in the presence of a monomer

M. The Cu(I) species disproportionates into a Cu(0) and Cu(II) species. The active species

reacts with the Cu(II) and gets deactivated. The resulting Cu(I) intermediate again

disproportionates again into Cu(0) and Cu (II) so that the activator and the deactivator are

constantly replenished. The disproportionation is benefitted by the usage of nitrogen containing

ligands, which stabilize the Cu(II) species. Polar solvents, dipolar aprotic liquids, ionic liquids,

alcohols or water also benefit this reaction. [22-26]

SET-LRP provides an excellent control over the molecular weight, dispersity, polymer

architecture or end group functionality and it shows several advantages to other controlled

living radical polymerizations. It is one of the more robust polymerizations and can be

performed in several solvents, like water, alcohols and even tequila. [26] It can be also used under

92

biological conditions like in sheep blood serum. [27] While monomers used in ATRP need to

have a group that stabilizes the radical like styrene or methacrylate, SET-LRP can also

polymerize non-activated monomers. So it is possible, to use monomers, which are not

polymerizable under ATRP conditions, like NIPAAM or vinyl chloride. [24, 25]

The mentioned methods can now be used to graft several different polymers to a microgel

surface. There are many polymers, which can be used, but this work only discusses a select few.

93

5.2 Aim

In this chapter, grafting experiments onto the surface of specific VCL based microgels are

reported. The goal is the formation of brush like structures on the microgel surface as shown in

scheme 5.4.

Scheme 5.4. Functionalization of the microgel shell.

Brush-like structures are formed when polymers are grafted from the microgel surface. When

the polymer is densely grafted onto the surface and crosslinked it is called a core/shell like

structure, since the brush polymers are not only located on the surface, they surround the

microgel as a continuous layer.

There are several advantages of the grafting from polymerization to synthesize core/shell

structures. The polymerization can be done at room temperature, when the core is still in a

swollen state. Since the reaction is initiated from oligoglycidol, the grafted polymers are

covalently bound to the core as opposed to a classic shell synthesis. In a classic shell synthesis,

a monomer and a crosslinker are polymerized to form a dense, crosslinked polymer shell around

the already existing particle core. The shell is not covalently bound to the core but merely

surrounds it. To form such a shell usually a crosslinker has to be added to the reaction while

this is not the case here.

As substrate a PVCL based microgel was chosen, which is copolymerized with oligoglycidol

macromonomers. The latter is located on the microgel shell. The primary alcohol groups can

be easily used or modified for the grafting-from polymerization.

PVCL

Oligoglycidol Macromonomer

Grafted Polymer

94

Several different monomers are used for the functionalization. They are shown in figure 5.1.

Figure 5.1. Different monomers that are used in the grafting from polymerization on PVCL

microgels.

One of these monomers is sulfobetain. Betains are zwitterionic molecules. They have a cationic

and anionic group within the molecule. The cation can be an ammonium group, while the anion

can be a carboxy-, a phosphonate- or a sulfonate group. There are already microgels, which

consist of zwitterionic molecules. They show several characteristics, which brings them

advantages in biological or medicinal applications.

For example, polycarboxybetain coated surfaces show a high resistance to unspecified protein

absorption. They can however easily be modified to let specific proteins bind to the surface,

while still having a high resistance to other proteins. [28, 29] Furthermore, zwitterionic microgels

can be used as reaction sites for the synthesis of metal nanoparticles. [30]

Styrene sulfonic acid (SSA) is another monomer, which can be used in a grafting-from

polymerization. Its polymer is a nonadsorbing polyelectrolyte and shows some antiviral

activity. [31] Because of its negative charge it is usually used in the deposition of multilayers on

a surface. Such layers can also be assembled on a microgel surface to modify its swelling degree

and behavior to an external stimulus. [32-34]

Di (ethylene glycol) ethyl ether acrylate (DEGA) and 2-methoxyethylacrylate (MEA) can also

be used. Like poly(ethylene glycol), those polymers show a very good biocompatibility.

Especially PMEA shows an excellent compatibility with blood, which is due to the mobility of

water in the polymer. [35-38]

95

NIPAAM is an attractive monomer, since its polymer shows temperature sensitive properties,

like PVCL, the building block of the used microgels. It can be used to synthesize core-shell

particles, since NIPAAM tends to self-crosslinking during the polymerization. [39]

Acrylonitrile is a monomer, which is commonly used in the production of fibers. Its polymer

can be modified with amidoxime groups which lead to fibers that show the ability to absorb

heavy metal ions. [40, 41] The fibers are also used as precursors in the formation of carbon fibers.

[42]

Several different grafting techniques are tried. The grafting-from redox polymerization with a

cerium species was used because the alkyl group next to the OH group can be converted to a

radical through the use of cerium ammonium nitrate. The second grafting technique is the

single-electron-transfer living radical polymerization. In a first step the alcohol group is

converted to an alkyl halide group which acts as an initiator in the second step, the actual SET-

LRP.

The aim is to incorporate different polymers into the microgel shell, which have different

properties and could thus lead to different applications. It is shown that the grafting of the

polymers from the surface is possible and that they are covalently bound to the microgel.

96


The microgels used are presented in chapter 3. PVCL based microgels are copolymerized with

different oligoglycidol macromonomers with vinyl benzyl alcohol as head group. The

synthesized microgel samples are further referred to as MG-x-y-A. X stands for the number of

glycidol repeating units in the macromonomer whereas y stands for the amount of

macromonomer used in mol% in relation to the used molar amount of VCL. A means that the

microgel was synthesized by batch synthesis. B means that it was synthesized by the continuous

method, which means that the crosslinker was added over a certain time after the addition of

the initiator to the reaction mixture.

The letter N s in the following tables stands for the number of repeating units of the used

monomer in relation to the number of assumed radicals formed.

The gravimetric yield is determined by weighing the sample and comparing the mass with the

expected mass at a monomer conversion of 100%.

Grafting-from polymerization with DEGA

Reaction at room temperature using MG-50-0.50-A

MG-50-0.5-A (99.97 mg, 0.15 mmol OH groups) is dispersed in H2O (7.1 mL) in a Schlenk

flask. Nitric acid (65%, x mL (see table 5.1)) is diluted with H2O (13 mL) and added slowly

dropwise to the dispersion. The mixture is frozen in liquid nitrogen, degassed in vacuum and

thawed. The entire process is repeated 3 times. Ceric ammonium nitrate (CAN) (y g (see table

5.1) is dissolved in H2O (1 mL), degassed for 10 minutes and added to the reaction mixture.

After 3 minutes of stirring, the monomer DEGA is added. The mixture is stirred overnight and

97

purified via dialysis for 3 days. After freeze-drying, the product is obtained as a white to yellow

powder. Table 5.1 lists the used amounts of chemicals for the different samples.

Table 5.1. Amount of educts used in the redox polymerization of DEGA using MG-50-0.5-A*.

Sample Degree of

activation N

Amount

CAN / g

(mol)

Amount

DEGA /

g (mol)

V(HNO3) /

mL

Gravimetric

Yield / %

DEGA-

MG0 0 20 /

3.91∙10-1

(2.08∙10-3) 0.08 0

DEGA-

MG1 68.97 5

5.70∙10-2

(1.04∙10-4)

9.79∙10-2

(5.20∙10-4) 0.08 72.2

DEGA-

MG2 68.97 10

5.70∙10-2

(1.04∙10-4)

1.96∙10-1

(1.04∙10-3) 0.08 86.5

DEGA-

MG3 68.97 20

5.70∙10-2

(1.04∙10-4)

3.91∙10-1

(2.08∙10-3) 0.08 100

DEGA-

MG4 41.38 5

3.42∙10-2

(6.24∙10-5)

5.87∙10-2

(3.12∙10-4) 0.05 100

DEGA-

MG5 41.38 10

3.42∙10-2

(6.24∙10-5)

1.17∙10-1

(6.24∙10-4) 0.05 66.6

DEGA-

MG6 41.38 20

3.42∙10-2

(6.24∙10-5)

2.35∙10-1

(1.25∙10-3) 0.05 60.4

DEGA-

MG7 27.59 5

2.28∙10-2

(4.16∙10-5)

3.91∙10-2

(2.08∙10-4) 0.03 9.7

DEGA-

MG8 27.59 10

2.28∙10-2

(4.16∙10-5)

7.83∙10-2

(4.16∙10-4) 0.03 25.4

DEGA-

MG9 27.59 20

2.28∙10-2

(4.16∙10-5)

1.57∙10-1

(8.32∙10-4) 0.03 84.3

DEGA-

MG10 10.00 50

8.27∙10-3

(1.51∙10-5)

1.42∙10-1

(7.54∙10-4) 0.01 0

* 99.97 mg (0.15 mmol OH groups)

98

Reaction at elevated temperatures using MG-50-0.50-A

The grafting-from polymerization at elevated temperatures (40 or 50 °C) is done analogous to

the reaction at room temperature. The amount of CAN, nitric acid and DEGA is chosen similar

to sample DEGA-MG6. The reaction temperature is chosen as 40 or 50°C. The name of the

synthesized products is DEGA-MG6-xx°C where xx stands for the synthesis temperature.

Reaction at room temperature with a continuous monomer addition using MG-50-0.50-A

The amount of CAN, nitric acid and DEGA is chosen similar to sample DEGA-MG6. The

microgel dispersion is put in a Schlenk flask and diluted with H2O (20 mL). Nitric acid (65%,

0.05 mL) is diluted in H2O (13 mL) and added slowly dropwise to the dispersion. The whole

mixture is frozen in liquid nitrogen, degassed in vacuum and thawed. The entire process is

repeated 3 times. Ceric ammonium nitrate (3.42∙10-2 g, 6.24∙10-5 mol) is dissolved in H2O (1

mL) and degassed for 10 minutes. DEGA (2.35∙10-1 g, 1.25∙10-3 mol) is dissolved in H2O (10

mL) and degassed three times. The CAN-solution is added to the reaction mixture and after 3

minutes of stirring, the DEGA is slowly added to the reaction mixture with a syringe pump.

The DEGA solution is added with a speed of 0.5 mL per hour. The synthesized product is called

DEGA-MG6-syringe pump.

Reaction at room temperature using MG-50-0.25-A.

The reaction conditions are similar to the reactions with the sample MG-50-0.5-A. For the

reactions, 100.01 mg (0.08 mmol OH groups) microgel are used. The product is obtained after

freeze drying as a white powder. Table 5.2 lists the used amounts of the chemicals for the

different samples.

99

Table 5.2. Amount of educts used in the redox polymerization of DEGA using MG-50-0.25-

A*.

Sample Degree of

activation N

Amount

CAN /

g (mol

Amount

DEGA /

g (mol)

V (HNO3) /

mL

Gravimetric

Yield / %

DEGA-

MG11 68.97 10

3.03∙10-2

(5.53∙10-5)

1.03∙10-1

(5.48∙10-4) 0.04 /

DEGA-

MG12 68.97 20

3.03∙10-2

(5.53∙10-5)

2.05∙10-1

(1.09∙10-3) 0.04 53.6

DEGA-

MG13 41.38 10

1.82∙10-2

(3.32∙10-5)

6.25∙10-2

(3.32∙10-4) 0.02 3.1

DEGA-

MG14 41.38 20

1.82∙10-2

(3.32∙10-5)

1.25∙10-1

(6.65∙10-4) 0.02 61.1

* 100.01 mg (0.08 mmol OH groups)

1H-NMR (D2O):

δ (ppm) = 0.937-1-139 (m, 3H, H-22), 1.16-1.98 (m, 12H, H-2, H-5, H-7, H-14), 2.07-2.31 (m,

1H, H-6), 2.31-2.66 (m, 2H, H-1), 2.68-3.40 (m, 3H, H-11, H-15), 3.40-3.92 (m, 15H, H-3, H-

4, H-12, H-13, H-18-21), 3.99-4.40 (m, 4H, H-10, H-17).

Grafting-from polymerization with MEA using MG-50-0.50-A

MG-50-0.50-A (99.97 mg, 0.15 mmol OH groups) is dispersed in H2O (7.1 mL) in a schlenk

flask. Nitric acid (65% x mL (see table 5.3)) is diluted with H2O (13 mL) and added slowly

dropwise to the dispersion. The whole mixture is frozen in liquid nitrogen, degassed in vacuum

100

and thawed. The entire process is repeated 3 times. Ceric ammonium nitrate (y mL (see table

5.3) is dissolved in H2O (1 mL), degassed for 10 minutes and added to the reaction mixture.

After 3 minutes of stirring, the monomer MEA is added. The mixture is stirred overnight at

room temperature and purified via dialysis for 3 days. After freeze-drying, the product is

obtained as a white to yellow powder. Table 5.3 lists the used amounts of chemicals for the

different samples.

Table 5.3. Amount of educts used in the redox polymerization of MEA using MG-50-0.50-A*.

Sample Degree of

activation N

Amount

CAN /

g (mol)

Amount

MEA /

g (mol)

V(HNO3) /

mL

Gravimetric

Yield / %

MEA-

MG0 0 20 /

2.71∙10-1

(2.08∙10-3) 0.08 0

MEA-

MG1 68.97 5

5.70∙10-2

(1.04∙10-4)

6.77∙10-2

(5.20∙10-4) 0.08 57.4

MEA-

MG2 68.97 10

5.70∙10-2

(1.04∙10-4)

1.35∙10-1

(1.04∙10-3) 0.08 3.6

MEA-

MG3 68.97 20

5.70∙10-2

(1.04∙10-4)

2.71∙10-1

(2.08∙10-3) 0.08 86.1

MEA-

MG4 41.38 5

3.42∙10-2

(6.24∙10-5)

4.06∙10-2

(3.12∙10-4) 0.05 20.2

MEA-

MG5 41.38 10

3.42∙10-2

(6.24∙10-5)

8.12∙10-2

(6.24∙10-4) 0.05 190.1

MEA-

MG6 41.38 20

3.42∙10-2

(6.24∙10-5)

1.62∙10-1

(1.25∙10-3) 0.05 35.8

MEA-

MG7 27.59 5

2.28∙10-2

(4.16∙10-5)

2.71∙10-2

(2.08∙10-4) 0.03 39.2

MEA-

MG8 27.59 10

2.28∙10-2

(4.16∙10-5)

5.41∙10-2

(4.16∙10-4) 0.03 0

MEA-

MG9 27.59 20

2.28∙10-2

(4.16∙10-5)

1.08∙10-1

(8.32∙10-4) 0.03 79.3

*(99.97 mg, 0.15 mmol OH groups)

101

1H-NMR (D2O):

δ (ppm) = 1.12-2.06 (m, 12H, H-2, H-5, H-7, H-14), 2.11-2.35 (m, 1H, H-6), 2.35-2.69 (m, 2H,

H-1), 2.82-3.30 (m, 3H, H-11, H-15), 3.30-3.44 (m, 3H, H-19), 3.51-3.81 (m, 9H, H-3, H-4 H-

12, H-13, H-18), 4.02-4.47 (m, 4H, H-10, H-17).

Grafting-From Polymerization with Sulfobetain using MG-50-0.75-A.


flask. Nitric acid (65%, x mL (see table 5.4)) is diluted with H2O (13 mL) and added slowly

dropwise to the dispersion. The whole mixture is frozen in liquid nitrogen, degassed in vacuum

and thawed. The entire process is repeated 3 times. Ceric ammonium nitrate (y g (see table 5.4)

is dissolved in H2O (1 mL), degassed for 10 minutes and added to the reaction mixture. After 3

minutes of stirring, the monomer sulfobetain-1 (SB) is added. The mixture is stirred overnight

and purified via dialysis for 3 days. After freeze-drying, the product is obtained as a white to

yellow powder. Table 5.4 lists the used amounts of chemicals for the different samples

102

Table 5.4. Amount of educts used in the redox polymerization of sulfobetain-1using MG-50-

0.75-A*.

Sample

Degree of

activation /

%

N

Amount

CAN /

g (mol)

Amount

SB /

g (mol)

V (HNO3) /

mL

Gravimetric

Yield / %

SB-MG1 70 20 1.63∙10-1

(2.92∙10-4)

1.66

(5.94∙10-3) 0.22 39.3

SB-MG2 70 30 1.63∙10-1

(2.92∙10-4)

2.49

(8.91∙10-3) 0.22 28.0

SB-MG3 70 50 1.63∙10-1

(2.92∙10-4)

4.15

(1.49∙10-2) 0.22 22.2

SB-MG4 70 80 1.63∙10-1

(2.92∙10-4)

6.64

(2.38∙10-2) 0.22 65.6

SB-MG5 70 100 1.63∙10-1

(2.92∙10-4)

8.30

(2.97∙10-2) 0.22 40.2

SB-MG6 40 20 9.32∙10-2

(1.70∙10-4)

0.95

(3.40∙10-3) 0.12 32.4

SB-MG7 40 80 9.32∙10-2

(1.70∙10-4)

3.80

(1.36∙10-4) 0.12 65.2

SB-MG8* 70 20 1.63∙10-1

(2.92∙10-4)

1.66

(5.94∙10-3) 0.22 0

* 200.00 mg, 0.44 mmol OH groups

** The reaction is performed analogous to the reactions SB-MG1 to SB-MG7 but with [2-

(methacryloylamino) ethyl]-dimethyl (3-sulfopropyl) ammonium hydroxide (sulfobetain-2) as

monomer.

1H-NMR (D2O):

δ (ppm) = 1.22-2.07 (m, 18H, H-2, H-5, H-7, H-14, H-16), 2.10-2.35 (m, 4H, H-21, H-22),

2.36-2.66 (m, 2H, H-1), 2.89-3.01 (m, 2H, H-3), 3.02-3.39 (m, 8H, H-19), 3.46-3.64 (m, 2H,

H-18), 3.68-3.87 (m, 7H, H-10, H-11-13), 4.04-4.54 (m, 4H, H-4, H-6, H-17).

103

Grafting-From Polymerization with Other Monomers Using MG-50-0.75-A.

In addition to the reactions mentioned above, several grafting-from polymerizations are

performed with the other monomers N-isopropyl acryl amide (samples N) and acryl nitrile

(samples A).


flask. Nitric acid (65%, 0.22 mL) is diluted with H2O (13 mL) and added slowly dropwise to

the dispersion. The mixture is frozen in liquid nitrogen, degassed in vacuum and thawed. The

entire process is repeated 3 times. Ceric ammonium nitrate (1.63∙10-1 g, 2.97∙10-4 mol

corresponding to 70% activation) is dissolved in H2O (1 mL), degassed for 10 minutes and

added to the reaction mixture. After 3 minutes of stirring, the monomer is added. The mixture

was stirred overnight and purified via dialysis for 3 days. After freeze-drying, the product is

obtained as a white to yellow powder. Table 5.5 lists the used amounts of chemicals for the

different samples.

104

Table 5.5. Amount of educts used in the redox polymerization of NIPAAM or acryl nitrile

using MG-50-0.75-A*.

Sample N

Amount of

monomer /

g (mol)

Gravimetric

Yield / %

N-MG1 20 0.67

(5.95∙10-3) 90.3

N-MG2 80 2.69

(2.38∙10-2) 74.7

A-MG1 20 0.32

(5.95∙10-3) 35.4

A-MG2 80 1.26

(2.38∙10-2) 65.9

* 200.00 mg, 0.44 mmol OH groups

Grafting-from polymerization with DEGA and sulfobetain-1 using MG-50-0.75-A


flask. Nitric acid (65%, 0.22 mL) is diluted with H2O (13 mL) and added slowly dropwise to

the dispersion. The whole mixture is frozen in liquid nitrogen, degassed in vacuum and thawed.

The entire process is repeated 3 times. Ceric ammonium nitrate (8.16∙10-2 g, 1.49∙10-4 mol;


105

added to the reaction mixture. After 3 minutes of stirring sulfobetain (0.83 g, 2.97∙10-3 mol

corresponding to a degree of polymerization N=20) is added. The mixture is stirred overnight

and purified via dialysis for 3 days. After freeze-drying, the intermediate product, which is

labeled as SD-MG1, is obtained as a white to yellow powder.

Afterwards, the intermediate product is redispersed in H2O (15 mL). Nitric acid (65%, 0.22 mL)

is added and the sample was frozen in liquid nitrogen. After degassing the sample and letting it

thaw, the process is repeated 3 times. Ceric ammonium nitrate (8.16∙10-2 g, 1.49∙10-4 mol


added to the reaction mixture. After 3 minutes of stirring DEGA (0.56 g, 2.97∙10-3 mol

corresponding to a degree of polymerization N=20 is added. The mixture was stirred overnight

and purified for 3 days by dialysis. After freeze-drying, the product SD-MG2 is obtained as a

white-yellow powder.

Esterification of Microgel MG-12-3.0-B with 2-bromo propionyl bromide; Synthesis of a

Multifunctional Macroinitiator

MG-VBA-12-3.0-B (1.00 g, 2.21 mmol OH groups) is dispersed in dichloromethane (75 mL).

Triethylamine (0.68 g, 6.63 mmol) is added and afterwards, 2-bromo-propionyl bromide (1.43

g, 6.63 mmol) is slowly added to the mixture. The reaction is stirred at room temperature

overnight. The sample is cleaned by first dialyzing it against ethanol and then against water for

3 days. The product is obtained as a white powder. The sample is referred to as MG-Br.

Gravimetric yield: 84.7%

106

SET-LRP of Styrene Sulfonic Acid using MG-Br

The multifunctional macroinitiator MG-Br (0.15 g) is dispersed in 5 mL H2O (5 mL) in a

Schlenk tube. Sodium 4-styrenesulfonate (x g (see table 5.6)), CuBr2 (10.5 mg, 0.05 mmol) and

Me6TREN (21.55 mg, 0.09 mmol) are added, whereas the dispersion turns slightly blue. The

reaction mixture is frozen in liquid nitrogen and degassed. After letting it thaw, the freeze-

thawing cycle is repeated 6 times. Under a nitrogen atmosphere, the activated copper wire is

added to the reaction mixture. It is stirred at room temperature overnight. For purification the

sample is dialyzed against 0.05 M hydrochloric acid until the sample turns white. Then it is

further dialyzed against water for 3 days and dried via freeze-drying. The product is obtained

as a white powder. Table 5.3.6 lists the amount of SSA and the gravimetric yield.

For the activation of the copper wire a mixture of DMSO (2 mL) and two drops of hydrazine

hydrate is degassed and thawed 3 times in another Schlenk tube. Copper wire (3 cm), wrapped

around a magnetic stirrer is put into the solution and stirred for 15 minutes. Afterwards, the

mixture is removed and the copper wire is washed 4 times with dry THF and dried in a vacuum.

Table 5.6. Amount of SSA used in the SET-LRP of styrene sulfonic acid.

Sample N n(SSA) / mol m(SSA) / g Gravimetric

Yield / %

SET-SSA-MG1 4 1.47∙10-3 0.60 59

SET-SSA-MG2 10 3.66∙10-3 0.38 68

SET-SSA-MG3 20 7.32∙10-3 0.76 49

107

SET-LRP of Sulfobetain using MG-Br

The multifunctional macroinitiator MG-Br (0.15 g) is dispersed in H2O (5 mL) in a Schlenk

tube. Sulfobetain (sulfobetain-1) (x g see table 5.7), CuBr2 (10.5 mg, 0.05 mmol) and Me6TREN

(21.55 mg, 0.09 mmol) are added, whereas the dispersion turns slightly blue. The reaction

mixture is frozen in liquid nitrogen and degassed. After letting it thaw, the freeze-thawing cycle

is repeated 6 times. Under a nitrogen atmosphere, the activated copper wire is added to the

reaction mixture. It is stirred at room temperature overnight. For purification the sample is

dialyzed against 0.05 M hydrochloric acid until the sample turns white. Then it is further

dialyzed against water for 3 days and dried via freeze-drying. The product is obtained as a white

powder. Table 5.7 lists the amount of sulfobetain and the gravimetric yield.

For the activation of the copper wire a mixture of DMSO (2 mL) and two drops of hydrazine

hydrate is degassed and thawed 3 times in another Schlenk tube. Copper wire (3 cm), wrapped

around a magnetic stirrer is put into the solution and stirred for 15 minutes. Afterwards, the

mixture is removed and the copper wire is washed 4 times with dry THF and dried in a vacuum.

Table 5.7. Amount of sulfobetain used in the SET-LRP of sulfobetain.

Sample N n(SB) / mol m(SB) / g Gravimetric

Yield / %

SET-SB-MG1 5 1.83∙10-3 0.51 28

SET-SB-MG2 10 3.66∙10-3 1.02 17

SET-SB-MG3 15 5.49∙10-3 1.53 83

SET-SB-MG4 20 7.32∙10-3 2.05 61

108


In chapter 4 it was described, how polyvinylcaprolactam microgels, copolymerized with

oligoglycidol macromonomers can be functionalized with several functional groups due to the

OH-groups on the microgel surface. In addition, there is also the possibility to use the hydroxyl

groups as initiators for further polymerizations. The result would be the formation of microgels

with brush-like appendages that show new or different properties. One possibility could be to

modify the microgels with hydrophilic and hydrophobic polymer chains on the surface which

potentially could make it dispersible in polar and apolar solvents.

One method of achieving this is a grafting-from redox polymerization with a cerium ion as an

initiator. Cerium (IV) salts can form redox systems with alcohol or thiol groups. The redox

polymerization with Ce was tested with several different monomers.

5.4.1 Grafting-From Polymerization on Microgels by Cerium induced Redox

Polymerization

The polymerization was performed with a Ce(IV) reducing agent ((NH4)2[Ce(NO3)6]) in the

presence of primary OH groups on the microgel surface. Scheme 5.5 shows an overview of the

synthesized polymer brushes.

Scheme 5.5. Grafting-from polymerization of different monomers on a PVCL/Oligoglycidol

microgel with different monomers by cerium induced redox polymerization.

PDEGA:

DEGA-MG0 to

DEGA-MG14

PMEA:

MEA-MG0 to

MEA-MG9

Polysulfobetain:

SB-MG1 to

SB-MG8

PNIPAAM

N-MG1 to N-MG2

Polyacrylonitrile:

A-MG1 to A-MG2

Ce (IV)

109

Functionalization of Microgels with Diethyleneglycol acrylate by Redox Poly-

merization[1]

Diethylene glycol acrylate is a water-soluble monomer. Different reactions were performed,

where the number of theoretical active sites and the number of theoretical repeating units was

varied. The analysis of the resulting products was done by Raman spectroscopy. Figure 5.2

shows Raman spectra of the unmodified microgel MG-50-0.5-A in comparison with the

modified sample DEGA-MG1.

Figure 5.2. Raman spectra of PDEGA and microgel before and after functionalization.

For the modified sample, there is a peak visible at 1730 cm-1, which corresponds to the ester

group of the DEGA repeating unit. The grafting-from polymerization is successful. To calculate

the exact amounts of the incorporated DEGA a calibration curve was prepared, by mixing the

sample MG-50-0.5-A with different amounts of the pure PDEGA. The mixture was analyzed

by Raman spectroscopy and the ratio of the intensity between the ester and the amide group

was plotted against the amount of substance ratio of both components. The curve is shown in

figure 5.3.

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

500100015002000250030003500

Inte

nsi

ty

Wave number / cm-1

MG-50-0.5-A

pure PDEGA

DEGA-MG1

1730 cm-1

110

Figure 5.3. Molar ester/amide ration in a mixture of MG-50-0.5-A and PDEG against the

intensity ratio.

The formula for the slope of the curve is given as

𝑛(𝐸𝑠𝑡𝑒𝑟)

𝑛(𝐴𝑚𝑖𝑑)= 0.930 ∗

𝐼(𝐸𝑠𝑡𝑒𝑟)

𝐼(𝐴𝑚𝑖𝑑) + 0.046.

With these results, the ratio of the intensity can be inserted and the actual amount of DEGA

groups relative to the VCL can be calculated and compared to the theoretical amount of DEGA.

Table 5.8 gives an overview for the different DEGA microgel samples.

y = 0,93x + 0,0458

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

0 1 2 3 4 5

n(E

ster)/

n(A

mid

e)

I(Ester)/I(Amide)

111

Table 5.8. Characteristic data for DEGA-MG samples.

Sample N Activation /

%

Ester / %

(found)

Ester / %

(theo) rH / nm PDI

pure microgel* 0 0 0 0 96.4 0.17

DEGA-MG0** 0 0 0 0 87.4 0.16

DEGA-MG1 5 68.97 33.2 45.8 113.9 0.18

DEGA-MG2 10 68.97 56.5 62.8 109.6 0.17

DEGA-MG3 20 68.97 76.8 77.1 128.6 0.24

DEGA-MG4 5 41.38 39.6 33.6 130.2 0.25

DEGA-MG5 10 41.38 35.9 50.3 102.5 0.16

DEGA-MG6 20 41.38 60.4 66.9 119.1 0.21

DEGA-MG7 5 27.59 0 25.2 113.9 0.18

DEGA-MG8 10 27.59 15.5 40.3 100.3 0.19

DEGA-MG9 20 27.59 48.6 57.4 103.4 0.16

DEGA-MG10 50 10.00 0 55.0 87.0 0.17

* The pure microgel refers to a sample without any oligoglycidol comonomer. The reaction conditions are similar to the other

reactions.

** The sample DEGA-MG0 refers to a sample, which was treated like the other samples, except no CAN was used during the

reaction.

The amount of the ester is given as a percentage in relation to the amount of the amide groups

of the VCL ring.

Several different reaction conditions were tried to vary the amount of polymer brushes on the

surface. The amount of CAN was varied, to give samples with a different number of side chains.

The amount of DEGA was varied, to synthesize side chains with different chain length. The

activation stands for activated glycidol groups in relation to the total amount of glycidol groups.

The equivalents of the amount of DEGA relates to the number of activated glycidol groups.

Sample DEGA-MG0 was used to determine if the DEGA shows any kind of reactivity towards

the microgel which is not caused by the reducing agent. The absence of PDEGA in the sample

confirms that the CAN is needed to initiate the reaction.

Overall the reactions follow a similar trend: A higher amount of DEGA in the feed leads to a

higher amount of PDEGA in the microgel (DEGA-MG1 to-MG3). For a degree of activation

of 10% (low concentration of CAN) no graft formation is observed even when high

concentrations of DEGA are used. By increasing the concentration of CAN so that 28% of

CH2OH should be activated a polymerization takes place. The polymerization efficiency is

112

dependent on the monomer concentration. By increasing the amount of DEGA the monomer

conversion increases (Samples DEGA-MG7, -8, -9). There are probably some side reactions,

like a reaction of CeIV with oxygen residue or some unforeseen reaction with the microgel or

impurities in the monomer, which can all lead to a decrease in the reaction efficiency. With

higher concentration of the Cerium or the DEGA, this side reaction become less significant. In

summary it can be said, that a higher degree of activation and a higher amount of monomer

leads to a higher monomer conversion.

The hydrodynamic radii of the samples were measured via dynamic light scattering. After the

treatment with the nitric acid, the microgel size slightly decreases (DEGA-MG0). After the

reaction, every sample except sample 10 has increased in size by 10 to 30 nm, while the PDI is

still low. It is assumed, that the size increase is due to the grafting of the PDEGA chains to the

microgel surface. Due to the relatively low number of repeating units per active center, the

increase in size should be negligible. The length of a C-C bond is 154 picometers which means

that samples with the highest amount of PDEGA (DEGA-MG3; DEGA-MG6: DEGA-MG9)

should merely show an increase in the radius of 6 nm. [43] But all samples show a higher increase

in the size. It is assumed that the microgels are poorly crosslinked in the shell which is not

properly detected during the DLS measurements. By adding the PDEGA side chains, the shell

becomes dense and can be detected better. This increase does not seem to follow any trend,

since samples with a higher amount of PDEGA do not show a larger microgel size. But it is

shown, that samples with the same number of repeating units become bigger with a higher

degree of activation.

The hydrodynamic radius of the modified microgels was measured dependent on the

temperature (figure 5.4).

113

Figure 5.4. Temperature sensitivity of microgels. Hydrodynamic radius in dependence of the

temperature before and after the modification with PDEGA.

Both samples show a comparable behavior in terms of temperature sensitivity.

Variation of the synthesis temperature

All polymerization reactions were performed at room temperature. In addition, several reactions

were performed at higher temperatures to analyze the influence on the conversion. The

conditions of sample DEGA-MG6 were chosen, but at 40 and 50°C. Table 5.9 shows the results.

Table 5.9. Results of the polymerization of PDEGA at different temperatures.

Sample Ester / %

(found)

Ester / %

(theo) rH / nm PDI

Gravimetric

yield / %

DEGA-MG6 60.4 66.9 119.1 0.212 72

DEGA-6-MG40°C 57.1 66.9 70.1 0.201 63

DEGA-6-MG50°C 62.2 66.9 1086 0.964 78

The reaction yield and the amount of ester in the sample don´t differ significantly from each

other. A higher temperature does not seem to influence the efficiency of the reaction. But the

hydrodynamic radii differ strongly. At a reaction temperature of 40°C, the size is actually

smaller than sample DEGA-MG6, which is synthesized at room temperature while at 50°C the

resulting microgels have an average size of 1 µm and a very high PDI. When the nanogels are

getting heated above the VPTT, they start to collapse. In addition, they also have a higher

tendency to aggregate, since the attracting van-der-Waals interactions are getting stronger.

0

20

40

60

80

100

120

140

15 25 35 45 55

rH

/ n

m

T / °C

MG-50-0.5-A

DEGA-MG-6

114

When the polymerization of the PDEGA chains starts, the microgel aggregates and it is

possible, that the polymerization leads to entanglements between singular particles. When the

temperature gets lowered below the VPTT; the particles cannot separate from each other,

because they are now physically connected to each other and the have formed large, hairy non-

spherical aggregates. The elevation of the temperature does not show any improvement so all

reactions were performed at room temperature.

Reaction at room temperature with a continuous monomer addition

Usually, the monomer is added to the reaction in a very short time. The addition time was

varied, to test if a continuous addition of the monomer leads to a more evenly distribution of

the PDEGA chains. The monomer was dissolved in water and slowly added to the activated

microgel dispersion with a syringe pump. The rate of addition is chosen as 0.5 mL per hour.

Table 5.10 shows the results.

Table 5.10. Results of the polymerization of PDEGA with different monomer addition

mechanisms.

Sample Ester / %

(found)

Ester / %

(theo)

rH /

nm PDI

Gravimetric

yield / %

DEGA-MG6 60.4 66.9 119.1 0.212 72

DEGA-MG6-

syringe pump 54.9 66.9 152.4 0.211 63

The results show a lower ester content in the sample and a lower yield, while the hydrodynamic

radius slightly increases. Since this is not a living polymerization, the termination reaction

increases with time, which leads to a decrease in the yield. So this method was not further

explored.

Reaction at room temperature using MG-50-0.25-A.

Another microgel, with a lower content of VBA-50 was also used in the polymerization, to

determine the influence of the amount of the available alkyl alcohol groups. For this, a microgel

sample with an amount of 0.25 mol% VBA-50 was used. Different amounts of CAN and DEGA

were used. The results are shown in table 5.11.

115

Table 5.11. Results of the polymerization of PDEGA with the microgel MG-50-0.25-A.

Sample N Activation /

%

Ester / %

(found)

Ester / %

(theo) rH / nm PDI

Gravimetric

yield / %

pure

microgel 0 0 0 0 178.51 0.097 /

DEGA-

MG11 10 68.97 32.1 45.3 125.5 0.401 53.6

DEGA-

MG12 20 68.97 6.1 62.4 186.7 0.380 3.1

DEGA-

MG13 10 41.38 24.7 33.2 157.2 0.377 61.1

DEGA-

MG14 20 41.38 12.3 49.8 153.0 0.371 12.4

Independent of the degree of activation, a high amount of DEGA leads to a very low yield in

the polymerization. Since there is now a lower number of active radicals in the mixture, the

influence of side reactions is stronger. It is assumed, that a high concentration of DEGA leads

to side reactions, which deactivate the active sites, without binding the DEGA to the microgel

surface.

With an increasing ester content, the hydrodynamic radius decreases. Because of the lower

amount of VBA-50, the size is bigger than the MG-50-0.5-A sample. Since PDEGA is more

hydrophobic, the functionalized microgel is more hydrophobic and it ejects more water, which

leads to shrinkage. This effect should in theory also be visible in samples with the higher VBA-

50 amount. At high amounts however, the overall swelling degree is lower, which is also caused

by a concentration of the crosslinker in the microgel core. So the change in hydrophilicity

caused by the PDEGA is less effective.

Functionalization of Microgels with 2-Methoxy Ethyl Acrylate by Redox Poly-

merization [1]

In addition to the modification with DEGA, samples were also polymerized with 2-methoxy

ethyl acrylate (MEA). The analysis of these microgels was also done by Raman spectroscopy

which is shown for one sample in figure 5.5.

116

Figure 5.5. Raman spectra of PMEA and microgel before and after functionalization.

A peak at 1730 cm-1 is visible for the modified sample which corresponds to the ester group of

the MEA molecule. The grafting-from polymerization is successful. Similar to DEGA, a

calibration curve was recorded. It is shown in figure 5.6.

Figure 5.6. Molar ester/amide ration in a PVCL/PMEA mixture against the intensity ratio.


𝑛(𝐸𝑠𝑡𝑒𝑟)

𝑛(𝐴𝑚𝑖𝑑)= 0.907 ∗

𝐼(𝐸𝑠𝑡𝑒𝑟)

𝐼(𝐴𝑚𝑖𝑑) + 0.054.

With this, the ester content and the yield of the polymerization could be determined. In addition,

the hydrodynamic radius was measured for every sample. Table 5.12 gives an overview over

the obtained results

0,00

0,20

0,40

0,60

0,80

1,00

500100015002000250030003500

Inte

nsi

ty

Wave number / cm-1

MG-50-0.5-A

pure PMEA

MEA-MG1

0

0,5

1

1,5

2

2,5

3

3,5

4

0 1 2 3 4 5

n(E

ster)/

n(A

mid

e)

I(Ester)/I(Amide)

1730 cm-1

117

Table 5.12. Results from the polymerization with MEA.

N Activation /

%

Ester /

% (found)

Ester /

% (theo)

rH / nm PDI

pure

microgel*

0 0 0 0 96.4 0.17

MEA-MG0** 20 0 0 0 87.4 0.16

MEA-MG1 5 68.97 32.3 45.8 155.3 0.25

MEA-MG2 10 68.97 15.6 62.8 92.2 0.18

MEA-MG3 20 68.97 73.6 77.1 93.0 0.13

MEA-MG4 5 41.38 14.1 33.6 95.4 0.18

MEA-MG5 10 41.38 64.6 50.3 108.6 0.14

MEA-MG6 20 41.38 39.6 66.9 100.5 0.16

MEA-MG7 5 27.59 12.3 25.2 93.3 0.18

MEA-MG8 10 27.59 0 40.3 88.4 0.15

MEA-MG9 20 27.59 51.9 57.4 100.0 0.12

* The pure microgel refers to a sample without any oligoglycidol comonomer. The reaction conditions are similar to the other

reactions.

** The sample MEA-MG0 refers to a sample, which was treated like the other samples, except no CAN was used during the

reaction.

Contrary to the DEGA samples, there is no clear trend visible. Especially the sample with 10

repeating units deviate strongly from the theoretical values. But it is evident, that the

functionalization with PMEA chains is successful. Apart from sample MEA-MG1 where

possibly some aggregation has taken place, the hydrodynamic radius shows only minor

changes. If the radius is correlated with the amount of ester in the sample it becomes apparent,

that the hydrodynamic radius slowly increases with increasing ester content.

The impact of the PMEA on the size is less pronounced as with PDEGA. Because MEA is

shorter than DEGA the shell is now less dense and the impact on the DLS measurements is

smaller. It can be assumed that different amounts of PMEA can be introduced on the surface of

the microgel without a substantial change in the size or dispersity.

Functionalization of Microgels with Sulfobetain by Redox Polymerization [2]

The grafting-from polymerization was studied with sulfobetain as a monomer too. In this case,

the degree of activation was mainly 70%. Sulfobetain is a molecule which among other

properties is resistant to an unspecific protein absorption. The idea behind this is to realize

118

microgels in which the sulfobetain is only located in the shell, where the repellant properties

are more useful if the microgel is to be used as a coating.

Analysis of the samples was done by 1H-NMR- and Raman spectroscopy. Figure 5.7 shows the

NMR spectrum.

Figure 5.7. 1H-NMR-spectrum of sample SB-MG2.

According to the NMR-spectrum, the sample contains a high amount of sulfobetain. Especially

the signal at 2.92 ppm is characteristic for the sulfobetain since it is assigned to the CH3-groups

bound to the nitrogen atom. A further analysis of the microgel via NMR is difficult. The

sulfobetain and the PVCL signals overlap. Because of the high amount of sulfobetain the PVCL

signals are very weak but are still visible, especially at 4.19 ppm. This peak is mainly assigned

to the proton next to the nitrogen atom of the VCL.

There is a possibility that the sulfobetain did not react with the glycidol groups and is merely

adsorbed into the microgel. But in that case the NMR would show signals corresponding to the

C-C double bond of the monomer at a chemical shift of 5.5 to 6.0 ppm, which is not the case.

To test this theory, a polymerization was done with a pure PVCL microgel, without the

oligoglycidol-macromonomer. Figure 5.8 shows the 1H-NMR spectrum of this sample. In this

case, the sample was not cleaned via dialysis.

ppm (t1)1.02.03.04.05.0

4.4

53

4.1

98

3.5

03

3.3

01

2.9

25

2.6

72

2.1

55

1.9

69

1.6

78

1.3

90

0.8

19

0.6

93

1.0

0

2.1

7

4.1

5

1.6

1

0.6

7

2.2

3

1.4

9

119

Figure 5.8. 1H-NMR-spectrum of a pure PVCL microgel after the redox polymerization with

SB.

In this spectrum, the signals for the double bonds at a chemical shift of 5.69 and 6.07 ppm are

clearly visible. Afterwards the sample was cleaned via dialysis where it was found that all the

sulfobetain has been washed out. The polymerization was not successful. The oligoglycidol

component is therefore essential to induce this kind of polymerization and the sulfobetain is

covalently bound to the microgel after the successful polymerization.

Because of the overlap of the NMR signals, the samples were further analyzed via Raman

spectroscopy to quantify the amount of sulfobetain present in the microgels. Figure 5.9 shows

the Raman spectrum of a microgel before and after the functionalization with sulfobetain.

Figure 5.9. Raman spectra of a microgel before and after the SET-LRP with SB.

ppm (t1)1.02.03.04.05.06.0

6.0

73

5.6

92

4.7

01

4.5

55

4.4

51

3.9

63

3.7

48

3.5

19

3.1

77

3.1

33

2.8

88

2.2

03

1.8

53

1.0

83

0.9

43

3.0

0

3.1

6

2.1

5

3.0

6

8.4

9

0.2

5

2.9

7

3.3

6

2.3

0

0.3

2

0.3

2

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

500100015002000250030003500

Inte

nsi

ty

Wave number / cm-1

MG-50-0.75-A

SB-MG4

1728 cm-1

1036 cm-1

120

Noticeable are the two new signals at 1036 cm-1, which is caused by the ester group in the

sulfobetain and at 1728 cm-1, which is caused by the SO3- group. The Raman spectra confirm

the presence of the polysulfobetain and the PVCL. For quantification, a calibration curve was

prepared by mixing fixed amounts of the sulfobetain monomer and a pure PVCL microgel. This

mixture was measured by Raman spectroscopy and the signal intensity of the ester signal of the

sulfobetain and the amide signal of the PVCL was compared. [44] The VBA-50 would have no

discernible effect on those two signals and is therefore negligible. The curve is shown in figure

5.10.

Figure 5.10. Molar ester/amide ratio in a PVCL/PSB mixture against the intensity ratio.


𝑛(𝐴𝑚𝑖𝑑𝑒)

𝑛(𝐸𝑠𝑡𝑒𝑟)= 0.839

𝐼(𝐴𝑚𝑖𝑑𝑒)

𝐼(𝐸𝑠𝑡𝑒𝑟)+ 0.0179

The size of the microgels was also measured via DLS. All results for the samples are now shown

in table 5.13.

0

2

4

6

8

10

12

14

16

18

20

0,00 5,00 10,00 15,00 20,00 25,00

n(A

mid

e)/

n(E

ster)

I(Amide)/I(Ester)

121

Table 5.13. Results of the grafting from redox polymerization with sulfobetain.

Sample N Ester / %

(found)

Ester / %

(theo) rH / nm PDI Gravimetric

Yield / %

pure

microgel 0 0 0 68.5 0.28 /

SB-MG1 20 68 82 72.09 0.40 39.3

SB-MG2 30 66 87 74.93 0.38 28.0

SB-MG3 50 73 92 85.11 0.44 22.2

SB-MG4 80 67 95 76.08 0.43 65.6

SB-MG5 100 77 96 73.08 0.45 40.2

The experimentally determined amount of ester is always lower, than the theoretical amount.

The highest possible amount is around 77%. As can be seen in table 5.13, the sulfobetain content

is relatively equal for all samples at around 70 to 80% regardless of the amount of used

monomer. This suggests, that there is an upper limit of how much sulfobetain can be grafted

onto the microgel. It might be, that the increasing amount of charges on the surface repels the

remaining monomers at some point, so that no additional sulfobetain molecule can be added.

All samples show a slight increase in the hydrodynamic radius. But this increase is between 4

and 17 nm which is negligible. The dispersity also increases. Presumably, the grafting process

was successful and the added chains now influence the microgel size. It is possible that the high

number of active sites can lead to a higher number of recombination reactions. In addition the

sulfobetain tends to form ionic bonds with each other. Thus it is possible that the PSB chains

on the surface tend to form bonds with each other or even with PSB chains from other particles,

which leads to aggregation. Because of the ionic nature of the polymer it is also possible that

some ionic cerium salts are still inside the sample which also contribute to a higher PDI. The

amount of sulfobetain on the surface does not seem to be correlating with the increase of the

dispersity. The temperature sensitivity of the samples was measured but no discernible trend

could be shown.

A sample was also analyzed via transmission electron microscopy (figure 5.11).

122

Figure 5.11. TEM image of sample SB-MG2.

Contrary to the samples of pure microgel (as seen in chapter 3), the analyzed microgels show a

good contrast because of the high concentration of polymers that is now grafted onto the

surface.

The gravimetric yield is rather low and does not correlate with the number of repeating units.

It ranges from 22 to 65%.

It is possible, that the high number of active sites leads to a low yield, which is why the reaction

was repeated with a lower degree of activation (40%). Table 5.14 shows the synthesized

samples.

Table 5.14. Results of the redox polymerization with sulfobetain with different amounts of

sulfobetain. Degree of activation: 40%.

Sample N Ester / %

(found)

Ester / %

(theo) rH / nm PDI

Gravimetric

yield / %

pure

microgel 0 0 0 68.50 0.28 /

SB-MG6 20 72 72 92.63 0.42 32.4

SB-MG7 80 81 91 175.42 0.50 65.2

Raman spectra show, that the functionalization was successful. Comparing the gravimetric

yield with the yield at higher degrees of activation, it can be seen, that the same number of

repeating units leads to a comparable conversion in both samples. This shows, that the number

of active sites does not influence the effectiveness of the reaction. But a stronger increase in the

hydrodynamic radius is visible. This is probable due to aggregation.

123

The redox polymerization does not seem to be usable on every kind of sulfobetain. A reaction

with [3-(methacryloyl amino) propyl]-dimethyl (3-sulfopropyl) ammonium hydroxide was

performed. Figure 5.12 shows the different sulfobetains.

Figure 5.12. Sulfobetain used in the samples SB-MG1-7 (left) and SB-MG8 (right).

Instead of an ester group, this molecule contains an amide group. The product was analyzed by

1H-NMR spectroscopy and showed no traces of the sulfobetain. Additionally the gravimetric

yield was around 0% which proves, that no reaction has taken place. This sulfobetain contains

an amide group. It is possible, that this group somehow suppresses the polymerization and

makes it unfavorable for the methacrylate group, to bind to the microgel.

Functionalization of Microgels with N-Isopropylacrylamide by Redox Polymerization

Two reactions with NIPAAm as a monomer were carried out. One with 20 equivalents and one

with 80 equivalents of monomer in relation to the amount of active sites. The analysis was done

via 1H-NMR spectroscopy. Figure 5.13 shows a spectrum for the sample N-MG2.

Figure 5.13. 1H-NMR spectrum of sample N-MG2.

ppm (t1)1.02.03.04.05.0

4.7

01

4.2

00

3.8

09

3.7

97

3.6

36

3.5

64

3.2

02

2.4

20

2.2

25

1.9

16

1.4

86

1.0

51

1.0

0

5.4

9

1.7

7

2.3

5

4.8

4

12.3

8

22.9

3

124

The signals at 1.05, 1.49, 1.92 and 3.81 ppm can be assigned to the PNIPAAM polymer, while

the signals at 2.22 and 2.42, 3.20 and 4.20 ppm belong to the PVCL microgel. The signal at

3.64 ppm is assigned to the oligoglycidol comonomer. The signals of the PVCL are weak in

comparison to the PNIPAAM because of the excess of the grafted polymer. There is no trace

of signals indicating the presence of vinyl groups which means that the NIPAM was

polymerized and is successfully grafted to the microgel as it would have been washed out during

the dialysis otherwise.

In addition, the hydrodynamic radii were measured. The results are shown in table 5.15.

Table 5.15. Hydrodynamic radius of the samples functionalized with NIPAAM.

Sample Repeating units rH / nm PDI

Pure microgel / 70.57 0.24

N-MG1 20 67.72 0.48

N-MG2 80 148.9 0.53

Sample N-1 shows negligible changes in the size. But the radius of sample N-2 is twice as big

as the original sample. This is in contrast to the hydrodynamic radius of the microgels, which

were modified with other monomers. It is possible, that this increase is due to the special nature

of the NIPAAm. When it polymerizes, it has a tendency for crosslinking. This means instead

of single brushes, which are formed with the other monomers, the NIPAAm forms a more shell

like structure. The dispersity increases, which might be a direct result of the self-crosslinking.

Functionalization of Microgels with Acrylonitrile by Redox Polymerization

Acrylonitrile sets itself apart from the other monomers used in the redox polymerization.

Acrylonitrile is soluble in water, while the corresponding polymer is not. It was used to test the

possibility of grafting hydrophobic polymers to the microgel surface.

It was shown, that during the reaction, the resulting product was insoluble and indispersable in

water, which is a clear indication that polyacrylonitrile has been formed. The product cannot be

analyzed via NMR spectroscopy, since it can no longer be dissolved or dispersed in any NMR

solvent. For analysis, a Raman spectrum of the samples was measured. Figure 5.14 shows the

Raman spectrum of sample A-MG2.

125

Figure 5.14. Raman spectra of a microgel before and after the redox polymerization with

Acrylonitrile.

At 2917 cm-1, there is a peak of high intensity visible, which is not shown in Raman spectra of

unmodified microgels. This peak can be assigned to the nitrile group of the acrylonitrile. It was

verified, that the polyacrylonitrile is bound to the microgel. The monomer has already been

washed out via dialysis in water. After that, the sample was dispersed in dimethyl formamide

and further dialyzed against DMF. The polymer is soluble in this solvent and should be washed

out, if it is not covalently bound to the microgel. After dialysis, the DMF was evaporated and

the residue was weighed, to check if any polymer has been washed out. No residue was found,

which means that the polymer is indeed bound to the microgel. In summary, it can be shown,

that in addition to hydrophilic polymers, also hydrophobic polymers can be grafted to the

microgel.

Functionalization of Microgels with DEGA and Sulfobetain by Redox Polymerization

The cerium induced polymerization can be used to functionalize the same microgel sample with

different polymers. If a CAN concentration is chosen which is sufficiently low then some

alcohol groups of the oligoglycidol macromonomer are not activated. After monomer A is

grafted on the microgel a second redox polymerization can be induced with monomer B with

the result that two varieties of polymer, each one consisting of a different repeating unit are

now located on the surface as is shown in scheme 5.6.

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

1,8

500100015002000250030003500

Inte

nsi

ty

Wave number / cm-1

A-MG1

A-MG2

2917 cm-1

126

Scheme 5.6. Modification of the microgel surface with two different polymers.

Ideally two polymers can be grafted which have different properties. The possibility for

preparation of such a microgel was now tested. The two chosen monomers were sulfobetain

and DEGA. Both polymers are hydrophilic in nature. For each polymerization, a degree of

activation of 0.35 was chosen. First, a grafting-from polymerization was done with sulfobetain.

The analysis was done via 1H-NMR spectroscopy. Figure 5.15 shows the spectrum.

Figure 5.15. 1H-NMR spectrum of sample SD-MG1.

Just like the other examined samples with sulfobetain, the spectrum shows signals which can

clearly be assigned to the sulfobetain molecule. The peak at 2.93 ppm is characteristic for the

methyl groups bound to the nitrogen atom. The first modification was successful. Afterwards,

the microgel was redispersed in water and CAN was again added to the reaction mixture and

the polymerization was now done with DEGA as monomer. From the product of this reaction,

again a 1H-NMR spectrum was measured, which is shown in figure 5.16.

ppm (t1)1.02.03.04.05.0

4.1

98

3.3

09

2.9

32

2.6

79

1.9

77

1.4

60

1.4

56

1.4

52

0.7

04

0.6

99

Polymer A Polymer B

Sulfobetain

127

Figure 5.16. 1H-NMR-spectrum of sample SD-MG2.

The signals at 0.60 to 1.00 ppm can be assigned to the alkyl group of the sulfobetain and the

DEGA. The signals at 3.30 and 3.93 to 4.20 ppm can be assigned to the CH2-groups of the

DEGA. The characteristic SB signal at 2.92 ppm is still visible in the spectrum. Signals from

sulfobetain and DEGA are visible in the spectrum, which confirms the hypothesis, that the

grafting-from redox polymerization can be successfully performed by sequential addition of

CAN/monomer 1 and CAN/monomer 2. The hydrodynamic radius of the sample was measured

before the reaction, after the polymerization with sulfobetain and after the reaction with DEGA.

They are listed in table 5.16.

Table 5.16. Hydrodynamic radii of the samples labeled SD.

Sample rH / nm PDI

Unmodified microgel 70.57 0.24

SD-MG1 137.3 0.49

SD-MG2 108.4 0.31

After the first modification, the radius nearly doubles in size and the PDI increases. This is

likely due to some aggregation of the microgel, attributed to the sulfobetain groups. After the

second modification, the microgel size decreases again, along with the PDI. There are several

possible explanations. Due to the redispersion process and the reaction, aggregated microgels

could be separated again. Additionally it is possible that the first polymerization with

sulfobetain is distributed uneven on the microgel shell. The reaction with DEGA leads to a more

ppm (t1)0.01.02.03.04.05.0

4.4

56

4.1

98

4.1

95

3.9

38

3.2

97

2.9

32

2.6

78

1.9

73

1.6

67

0.8

58

Sulfobetain

DEGA

128

evenly modification of the surface. It could also be, that the grafting of PDEGA somehow

disturbs the ionic bonds between the SB molecules so that the aggregation of the particles which

is due to the bonds developed by the SB is reduced.

In conclusion it can be said that the grafting-from redox polymerization with a cerium salt as a

reducing agent is possible with different monomers. There is only slight change in the size of

the microgels but the dispersity increases. Successful grafting-from polymerization was

achieved with DEGA, MEA, sulfobetain, NIPAAM and acrylonitrile, while experiments with

styrene sulfonic acid and N-vinylimidazole were not successful.

5.4.2 Grafting-from Single-Electron-Transfer Polymerization

Several cases of the cerium induced polymerization show, that not every monomer can be

polymerized and grafted to microgels in water as a solvent Styrene Sulfonic acid for example

could not be grafted from the surface by cerium induced redox polymerization. So an alternative

method was employed: The single-electron-transfer living radical polymerization (SET-LRP).

It can be used with a variety of different monomers. Before the SET-LRP can take place, the

microgel has to be functionalized with an initiating group like a α-bromo-propionyl group

(scheme 5.7).

Scheme 5.7. Grafting-from polymerization of different monomers on a PVCL/oligoglycidol

microgel with different monomers by SET-LRP.

In contrast to the cerium induced polymerization, the SET-LRP cannot be controlled in regard

to the number of grafted polymer chains. The amount of cerium used correlates with the number

Polysulfobetain: SET-SB-MG1 to SET-SB-MG4

Polystyrene sulfonic acid: SET-SSA-MG1 to SET-SSA-MG3

SET-LRP

129

of active radicals, while during the SET-LRP every initiator group bound to the microgel is a

possible site for a side chain. To control the number of active sites, the number of initiating

groups introduced into the colloidal system has to be controlled.

Initiating groups are introduced via esterification of the hydroxyl groups on the surface of

PVCL/oligoglycidol microgels with 2-bromo propionyl bromide (scheme 5.8).

Scheme 5.8. Esterification of an OH-group with 2-bromopropionylbromide.

The carbonyl bromide readily reacts with the OH-group. The triethylamine is used to bind the

freed HBr molecules. The product is more hydrophobic than the unfunctionalized microgel and

partly precipitates during the dialysis. The analysis was done via Raman spectroscopy (figure

5.17).

Figure 5.17. Raman spectrum of a microgel modified with 2-bromopropionylbromide (used

microgel: MG-12-3.0-B).

At 1750 cm-1, there is now a small peak visible, which corresponds to the ester group, which is

formed during esterification. It is assumed that because of the ease of the reaction, the

conversion of the hydroxyl groups is 100%. The size of the microgels was analyzed and is

shown in table 5.17.

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

500100015002000250030003500

Inte

nsi

ty

Wave number / cm-1

1750 cm-1

130

Table 5.17. Hydrodynamic radius before and after the functionalization with isopropyl

bromide.

Sample rH / nm PDI

MG-12-3.0-B 121.96 0.26

MG-Br 67.48 0.49

After functionalization, the hydrodynamic radius decreases, while the dispersity increases. It is

assumed, that because of the increased hydrophobicity, the microgel expels more water and

shrinks. The dispersity increases because the hydroxyl and after functionalization the initiating

α-bromo-propionyl groups are unevenly distributed on the microgel surface. In addition the

dispersion in several different solvents and the drying process lead to aggregation.

Functionalization of Microgels with Styrene Sulfonic Acid by SET-LRP

A microgel with initiating sites was used for SET-LRP of styrene sulfonic acid (SSA) as

monomer. Different amounts of SSA were used to test, if the amount of monomer influences

the grafting. In addition, a reaction without initiating groups in the microgel was analyzed.

Figure 5.18 shows the Raman spectrum of several samples after modification with SSA.

Figure 5.18. Raman spectrum of samples after the SET-LRP with SSA.

There is a peak of large intensity at 1600 cm-1, which can be assigned to the phenyl group of

the styrene repeating units, while the signal at 1040 cm-1 correlates with the sulfonate vibration.

The reaction without an initiating group did not show the characteristic SSA peak; the reaction

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

500100015002000250030003500

Inte

nsi

ty

Wave number / cm-1

SET-SSA-

MG1

SET-SSA-

MG2

SET-SSA-

MG3

1600 cm-1

131

did not take place. Figure 5.19 gives an enhanced view of the phenyl ring vibration for all

samples.

Figure 5.19. Raman spectrum of the styrene signal of all SET-SSA-MG samples.

Since the amide and the styrene vibration overlap, it is not possible to exactly calculate the

microgel/SSA-ratio. But it can be seen, that the amount of SSA increases with the amount of

monomer used. Table 5.18 lists the hydrodynamic radii of the different samples.

Table 5.18. Results for the samples after the SET-LRP with SSA.

Sample N rH / nm PDI Zetapotential / mV

MG-Br / 67.48 0.49 0

SET-SSA-MG1 4 154.15 0.54 -31.4±4.0

SET-SSA-MG2 10 205.10 0.44 -54.4±3.8

SET-SSA-MG3 20 400.20 0.51 -51.8±5.4

With an increase in the number of repeating units, the hydrodynamic radius increases, which is

probably due to the polymer brushes, which are grafted onto the microgel shell. The dispersity

also increases. It can be assumed, that due to the high density of initiating groups on the surface,

some of them are more sterically hindered than other groups. This leads to polymer brushes

with differing and longer chain lengths and an uneven shell surface.

In addition, the zetapotential of the microgels was measured. While the sample without SSA

shows a zetapotential of around 0, the samples SET-SSA-MG1 to MG3 show a negative

potential ranging from 30 to 55 mV. This is probably due to the sulfonic acid groups of the SSA

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

15001550160016501700

Inte

nsi

ty

Wave Number / cm-1

SET-SSA-MG1

SET-SSA-MG2

SET-SSA-MG3

132

now located on the surface. This is a further proof for the success of the reaction. A temperature

sensitivity of the modified samples could not be measured.

Functionalization of Microgels with Sulfobetain by SET-LRP

The SET-LRP was also attempted with a sulfobetain monomer. As mentioned in 5.2 the

successful grafting of sulfobetain in controllable amounts is desired because of its antibacterial

properties. Several samples with different amounts of monomer were analyzed. Figure 5.20

shows several Raman spectra of the products.

Figure 5.20. Raman spectra of samples after the SET-LRP with SB.

What can be seen is a peak at 1750 cm-1, which corresponds with the signal, which is caused

by the ester group in the sulfobetain. In addition, there is also the signal at 1040 cm-1, which is

caused by the sulfonate group. Figure 5.21 shows the signal of the sulfonate group for all

samples.

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

500100015002000250030003500

Inte

nsi

ty

Wave number / cm-1

MG-Br

SET-SB-MG2

SET-SB-MG4

1750 cm-1

1040 cm-1

133

Figure 5.21. Raman spectra of the sulfonate signal of all SET-LRP-SB samples.

A higher amount of monomer in the reaction leads to signal of higher intensity in the spectra,

which in turn means that the amount of sulfobetain in the sample directly correlates with the

amount of sulfobetain in the feed. With the calibration curve from figure 5.10, it is now possible,

to calculate the amount of SB in the sample. This is listed in table 5.19, along with the microgel

sizes.

Table 5.19. Results for the samples after the SET-LRP with SB.

Sample N Ester / %

(found)

Ester / %

(theo) rH / nm PDI

Zetapotential /

mV

unmodified

microgel 0 0 0 67.48 0.491 0

SET-SB-MG1 5 10 66 189.17 0.416 -9.85±4.61

SET-SB-MG2 10 26 83 145.70 0.441 -2.62±3.74

SET-SB-MG3 15 80 87 109.14 0.398 -4.16±3.61

SET-SB-MG4 20 92 93 155.89 0.444 -9.35±4.24

After the polymerization, the hydrodynamic radius has increased significantly. There might be

several factors responsible. Since the brushes contain positive and negative ionic groups it is

possible, that the singular brushes crosslink through ionic interactions so that some particles

crosslink with each other. The zetapotential was measured but it was low in the functionalized

samples. They are around zero so the effect of the grafted polymers on the zetapotential is

negligible.

0

0,1

0,2

0,3

0,4

0,5

0,6

980 1000 1020 1040 1060 1080

Inte

nsi

ty

Wave number / cm-1

MG-Br

SET-SB-MG1

SET-SB-MG2

SET-SB-MG3

SET-SB-MG4

20

5

10

15

134

The temperature sensitivity of a sample was measured to test if the microgel behavior in

dependence of the temperature has changed after the modification. Figure 5.22 shows the

temperature sensitivity of a microgel before the modification with the alkyl halide and after the

SET-LRP with 20 equivalents of monomer.

Figure 5.22. Size (left) and polydispersity index (right) in dependence of temperature for the

microgel MB-12.3.0-B before and after SET-LRP with sulfobetain (SET-SB-MG4).

Both microgels show no difference in their temperature sensitivity. The sulfobetain is located

as brushes on the surface and is not temperature sensitive. Therefore it should not influence the

change in temperature of the VCL core. Since the core is not changed during the modification,

the temperature sensitivity remains unchanged unless a temperature sensitive polymer is grafted

on the surface. Sulfobetain does have a temperature sensitivity but the UCST is at 15°C so there

should be no discernible effect above this temperature. Even then, the sensitivity of the core

remains unchanged.

A sample was also analyzed via transmission electron microscopy (figure 5.23).

0

20

40

60

80

100

120

140

160

180

200

15 25 35 45 55

rH

/ n

m

T / °C

MG-12-3.0-B

SET-SB-MG4

135

Figure 5.23. TEM image of sample SET-SB-MG4.

Contrary to the samples of unfunctionalized microgel (as seen in chapter 3), the analyzed

microgels show a good contrast. Because of the high concentration of polymers that is now

grafted onto the surface.

Polysulfobetain brushes can be fixed on the microgel surface by redox polymerization with

CeIV and by Set-LRP. Those methods can be compared directly. By using the cerium induced

method the hydrodynamic radius of the microgels stays constant while the dispersity slightly

increases. The SET-LRP method leads to particle aggregation and microgels with a high

dispersity. The gravimetric yield of both methods cannot be compared as no direct trend can be

observed. In both cases the yield varies strongly. But it seems that at higher SB concentrations

the conversion of the monomer is higher, when SET-LRP is applied. At higher concentrations

of monomer the grafting-from efficiency is higher with the SET-LRP method as the found ester

content is nearly as high as the theoretical amount while the ester content in the redox

polymerization samples is always at least 10% lower than the theoretical amount.

136


It could be shown, that microgels modified with oligoglycidol macromonomers can be used for

further modification to graft polymer chains to the microgel surface. This can be done with

several different techniques. It is possible to use cerium salts for a redox polymerization to graft

different monomers, like DEGA, MEA, sulfobetain, NIPAAM or acrylonitrile but not styrene

sulfonic acid or vinyl imidazole. By changing the cerium content, it is possible to change the

number of polymer chains, grafted to the surface. The length of the chains can also be varied.

Apart from the acrylonitrile modified microgels, the other samples are dispersible in water.

In future works the synthesis of an amphiphilic colloidal system can be researched. It is possible

that hydrophilic (like PDEGA) and hydrophobic (like polyacrylonitrile) polymer chains can be

grafted on the same particle. These microgels should be stable in polar and apolar solvents.

Scheme 5.9 shows a schematic overview.

Scheme 5.9. Microgels with hydrophobic and hydrophilic chains in polar and apolar solvents.

The idea is, that the hydrophilic chains are soluble in the aqueous phase, while the hydrophobic

chains are collapsed in the microgel shell. By switching to an apolar solvent, the hydrophobic

chains stretch, while the hydrophilic ones collapse. The chains serve as some kind of stabilizing

agent, which leads to a colloidal system being dispersed in both kinds of solvents.

Beside a modification of microgels by CeIV catalyzed radical polymerization of suitable

monomers SET-LRP can be used for microgels functionalized with initiating sites (α-bromo-

137

propionyl groups). Contrary to the redox polymerization, the number of grafted polymer chains

can be controlled by the number of initiating sites.

Sulfobetain and SSA have been tried in the SET-LRP with microgels. So far, all monomers

showed a successful polymerization on the surface of the microgels. The number of grafted

polymers is dependent on the number of initiating sites bound to the microgel. It is possible to

polymerize monomers, which are not accessible by cerium induced redox polymerization. For

example SSA can be polymerized by SET-LRP while the polymerization of SSA in the presence

of CeIV was unsuccessful. All synthesized core-shell microgels showed an increase in size.

The next step now would be the grafting of very long polymer chains onto the microgels so that

the dispersion properties would be influenced by the brushes on the surface.

138

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6. Summary

The aim of this work was to realize a new route for a surface tailored microgels by

copolymerizing polyvinylcaprolactam with oligoglycidol macromonomers and to analyze the

microgels and modify them with different functional groups and polymers.

In the first part, microgels were synthesized and their properties like the size and the thermal

responsiveness were analyzed. It was shown, that with a higher amount of comonomer or a

longer oligomer chain, their size as well as the temperature sensitivity decrease, while the

colloidal stability increases. Calorimetric measurements were carried out and it was shown that

by using increasing amounts of macromonomer, the polymerization process gets retarded.

Specifically the vinyl benzyl head group is responsible for the retardation. Only the

polymerization of the VCL is retarded but not of the BIS, which leads to microgels which are

strongly crosslinked in the core but only very loosely in the shell. By using a variation of head

groups it was shown that the vinyl benzyl group shows the highest incorporation efficiency of

the analyzed samples.

The incorporation could only be done up to a certain amount, before the microgels became too

small. So a different synthesis method was employed in which the crosslinker was added during

the polymerization process after the addition of initiator. The first method leads to colloidal

networks, which are highly crosslinked in the core but less crosslinked in the shell, while the

second method leads to a network, which is evenly crosslinked throughout the whole microgel.

The latter method leads to systems, where the size is not controlled by the amount of

macromonomer, but the number of repeating units. The temperature sensitivity is also constant

regardless of the introduced oligoglycidol amount. It was possible, to introduce a larger amount

of macromonomer into the microgels than by using the first method. Both methods show

advantages and disadvantages over the other. Transverse relaxation measurements could prove,

that in any case, the oligoglycidol macromonomer was located in the microgel shell.

It could be shown that the microgel size, colloidal stability and temperature responsibility can

be tuned through the variation of the oligoglycidol macromonomer amount during the synthesis.

The location of the OH groups on the surface makes them available for further

functionalization.

The second part discusses the modification of the hydroxyl groups with several different

functional moieties, such as allyl-, vinyl sulfonate- and thiol groups. It was shown, that it was

possible to functionalize the OH groups with the mentioned groups. Furthermore, it could be

shown, that the amount of conversion could be controlled by the reaction conditions. Not every

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OH-group has to be modified, so it is possible to introduce several different functionalities onto

the same particle. The properties of the modified microgels were analyzed. In almost all samples

the size and the dispersity increased. The increase in the dispersity is attributed to two reasons.

First the microgels are dried and redispersed in different solvents several times which leads to

the aggregation and entanglement of some particles which is hard to reverse. Second, because

of the conversion there are fewer OH groups on the surface that might provide steric protection

against aggregation. The modified microgels still displayed a temperature sensitivity similar to

the unfunctionalized microgel, suggesting that the functional groups have no effect on the

hydrophilicity of microgels. The modified microgels can now be used in several applications

for example as crosslinkers in the formation of hydrogels.

In the third part, the possibility of grafting polymers onto the microgel shell was investigated.

This was done by testing two different modes of grafting-from polymerization: A cerium

induced redox polymerization and a single-electron-transfer living radical polymerization, in

which copper is used as the activator. Several different monomers were tested with the different

polymerization techniques. One advantage is that the polymerization can be carried out in water

since the microgels are dispersible in this solvent.

It was possible to graft polymers onto the surface via cerium induced polymerization. It was

easily controllable, because the number of active sites could be tuned by the amount of used

Ce(IV) salts. The modification worked for the monomers sulfobetain, NIPAM, DEGA, MEA

and acrylonitrile while it was not successful for poly (styrene sulfonate). The modified

microgels always show an increase in their size. It is not dependent on the amount of polymer

grafted on the surface. The dispersity also increases slightly but is nearly constant for most

samples. Since the number of active sites can be controlled it is easy to introduce different

polymer chains onto the surface. A microgel could be modified with PDEGA chains first and

afterwards with hydrophobic polyacrylonitrile chains. But not every monomer can be

polymerized with that system.

In contrast, the SET-LRP mechanism works with monomers which did not polymerize under

redox polymerization conditions, such as sodium styrene sulfonate and sulfobetain. The

disadvantage over the redox polymerization is its lack of control. To induce a SET-LRP, the

microgel has to be modified with alkyl halide groups. The polymerization happens potentially

at every initiating site. So the control is only possible by controlling the amount of used

monomer or the number of converted hydroxyl groups. In order to bind different polymers on

the microgel with SET-LRP only a fraction of the OH groups has to be changed into alkyl halide

groups. This process has to be repeated after the first grafting-from polymerization. The

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microgels can be easily modified with a propionyl bromide group but there is a high increase

in their dispersity afterwards. After the SET-LRP the hydrodynamic radius of the microgels has

increased significantly while the dispersity remains high.

PVCL microgels modified with oligoglycidol macromonomers are easily tunable as the size,

the colloidal stability and the temperature sensitivity as well as the morphology can be

controlled. They can be modified with several functional groups. It is also possible to graft

different polymer brushes onto the microgel surface.

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7. Nomenclature

Å - Ångström

AAEM - Acetoacetoxy Ethyl Methacrylate

AGE - Allyl Glycidyl Ether

AMPA - 2, 2´-Azobis [2-Methyl-Propionamidine] Dihydrochloride

ATRP - Atomic Transfer Radical Polymerization

BIS - Methylenebisacrylamide

CAN - Ceric Ammonium Nitrate

CDCl3 - Deuterated Chloroform

CSC - 2-Chloroethane Sulfonyl Chloride

D2O - Deuterated Water

Da - Dalton

DCM - Dichloromethane

DEGA - Di (Ethylene Glycol) Ethyl Ether Acrylate

δ - Chemical Shift

DLS - Dynamic Light Scattering

DMF - N, N´-Dimethyl formamide

DMSO - Dimethyl sulfoxide

DTPA - 3,3´Dithiopropionic Acid

Eq - Equivalent

EEGE - Ethoxy Ethyl Glycidyl Ether

F-FFF - Flow Field-Flow Fractionation

g - Gram

GMA - Glycidyl Methacrylate

GPC - Gel Permeation Chromatography

h - Hour

H2O - Water

HCl - Hydrochloric Acid

HClO4 - Perchloric Acid

HAM - Hydroxy Ethyl Methacrylamide

HNO3 - Nitric Acid

HV - High Vacuum

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Hz - Hertz

IADME - Itaconic Acid Dimethyl Ester

ICl - Iodo Chloride

KOtBu - Potassium-Tert-Butanolate

λ - Wavelength

LCST - Lower Critical Solution Temperature

M -Molar

MEA - 2-Methoxy Ethyl Acrylate

mg - Milligram

MHz - Megahertz

mm - Millimeter

Mexp - Experimentally Determined Macromonomer Content

Mn - Number Average Molecular Weight

Mtheo - Theoretical Incorporated Macromonomer Content

mV - MilliVolt

Mw - Weight Average Molecular Weight

N - Number of Repeating Units

NaCl - Sodium Chloride

NaI - Sodium Iodide

NaOH - Sodium Hydroxide

NIPAAm - N-Isopropyl acrylamide

nm - Nanometer

NMR - Nuclear Magnetic Resonance Spectroscopy

PBS - Phosphate Buffered Saline

PDEGA - Poly (Di Ethylene Glycol Ethyl Ether Methacrylate)

PDI - Polydispersity Index

PEG - Poly (Ethylene Glycol)

PEGMA - Poly [Ethylene Glycol-Methacrylate]

PG - Polyglycidol

PMEA - Poly 2-Methoxyethylacrylate

PNIPAAM - Poly (N-Isopropyl Acrylamide)

ppm - Parts per Million

PS - Polystyrene

PVCL - Poly (N-Vinylcaprolactam)

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RAFT - Reversible Addition-Fragmentation Chain Transfer

rH - Hydrodynamic Radius

rpm - Rounds per Minute

SDS - Sodium Dodecyl Sulfate

SEC - Size Exclusion Chromatography

SET-LRP - Single-Electron-Transfer Living Radical Polymerization

SEM - Scanning Electron Microscopy

T - Temperature

tBGE - tert-Butylglycidylether

TEA - Triethylamine

TEM - Transmission Electron Microscopy

THF - Tetrahydrofuran

UCST - Upper Critical Solution Temperature

UV - Ultra Violet

VBA - Vinyl Benzyl Alcohol

VCL - N-Vinylcaprolactam

VIm - N-Vinylimidazole

VIS - Visible

VPTT - Volume Phase Transition Temperature

SB - [2-(Methacryloyloxy) Ethyl]-Dimethyl (3-Sulfopropyl) Ammonium

Hydroxide

SSA - Sodium 4-Styrenesulfonate

V - Volume

147

Danksagung

Ich möchte mich hier bei allen Leuten bedanken, die mir während meiner Promotion geholfen

und beigestanden haben.

Zuerst möchte ich Professor Dr. Andrij Pich danken, dass er mir die Möglichkeit gegeben hat,

unter ihm meine Arbeit anzufertigen. Desweiteren danke ich ihm für die Unterstützung, Hilfe

und Korrekturen, die er mir während meiner Arbeit hat zukommen lassen.

Zudem danke ich Professor Dr. Martin Möller für die Möglichkeit, am DWI zu promovieren

und dass er sich bereit erklärt hat, der Zweitkorrektor dieser Arbeit zu sein

Ein sehr großer Dank geht an Herr Keul, den ich nicht nur sehr oft wegen verschiedenster

Fragen zu Polyglycidol besuchen konnte, sondern der mir auch sehr mit der Korrektur meiner

Dissertation und Veröffentlichung geholfen hat.

Auch Dominik Schmitz und Andreea Balaceanu danke ich für die Hilfe mit der Korrektur

meiner Dissertation.

Sascha Pargen danke ich für die endlose Geduld bei meinen vielen Fragen zum Thema

Polyglycidol.

Rainer Haas danke ich für die große Hilfe in so vielen verschiedenen Dingen, dass ich sie gar

nicht alle aufzählen kann.

Herr Walter Tillmann denke ich für seine stete Hilfe bei der Messung und Auswertung von

Raman- und IR-Spektren.

Ich danke Justine Couthouis und Blanca Ines für ihre stete Hilfe bei Fragen zur SET-LRP.

Marina Richter und Huihui Wang danke ich für ihre Hilfe beim Umgang mit dem Tensiometer.

Danke an Claudia Formen für die Hilfe bei der UV/Vis Spektroskopie und auch ansonsten für

die angenehme Stimmung mit ihr.

Vielen Dank an Professor Demco und Andreea Balaceanu für deren Hilfe bei verschiedenen

NMR-Messungen.

Helga Thomas und Renate Jansen danke ich für die Möglichkeit, die Plasmaanalage zu

benutzen und deren Hilfe bei der Benutzung dieser.

148

Ich danke den Auszubildenden Fabian Deckwirth, Corinna Storck und Sabrina Mallmann dafür,

dass sie mich im Labor unterstützt haben und ich mit ihnen stets eine spaßige

Arbeitsatmosphäre genießen konnte. Besonders danke ich Sabrina für ihre Hilfe, um

erfolgreiche Bilder mit dem SU-9000 aufzunehmen.

Ich danke meinen unzähligen Bachelor- und Masterstudenten, die ich bei der Anfertigung ihrer

Arbeiten und Durchführung ihrer Praktika betreuen durfte. Das sind Ayse Yalcin, Valentin Fell,

Niklas Kinzel, Andrea Melle, Vi Tran, Thorsten Palmer, Bastian Fenger, Carel Kwamen, Anja

Hoffman, Lena Henkel, René Büttgen, Andreas Hoffmann, Nadine Daleiden, Thomas

Göttlinger und ganz besonders Saskia Inga Christamaria Gröer.

Ich danke wirklich allen Leuten des AK Pich und des DWI, nicht nur für die super

Arbeitsatmosphäre, sondern auch für die tolle Zeit überhaupt mit allen, die das Arbeiten und

meist auch die Freizeit immer zu einem Vergnügen gemacht haben, ganz besonders Dominik

Schmitz, Thomas Zosel, Andrea Melle, Christian Herbert und Dazril Phua. Danke für den

ganzen Spass.

Zum Abschluss danke ich den Leuten am meisten, mit denen ich jahrelang ein Labor geteilt

habe und die zu meinen Freunden wurden. Vielen Dank an Dominic Kehren, Andreea

Balaceanu, Ricarda Schröder, Thorsten Palmer und Wenjing Xhu. Ihr wart tolle Laborkollegen.

Mit euch war die Arbeitszeit immer spaßig und irgendwas zum Lachen oder Reden gab es

immer. Vielen Dank dafür, Labor 3.04/3.05!!!

Diese Arbeit wurde in Teilen am Center for Chemical Polymer Technology CPT durchgeführt,

welcher von der EU und dem Bundesland Nordrhein-Westfalen unterstützt wird (grant no.

EFRE 30 00 883 02).

149

Schlusserklärung

Hiermit erkläre ich, dass ich die vorliegende Arbeit selbstständig verfasst und keine anderen

als die hier angegebenen Quellen und Hilfsmitteln benutzt habe.

Ferner erkläre ich, dass ich nicht anderweitig mit oder ohne Erfolg versucht habe, eine

Dissertation einzureichen oder mich einer Doktorprüfung zu unterziehen.

Aachen, den 16.06.2017

……………………………………………………………………

Christian Willems

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