Defined Comonomer Re-Feeding During the Metallocene-Catalyzed Copolymerization of...

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Defined Comonomer Re-Feeding During theMetallocene-Catalyzed Copolymerization of 10-Undecene-1-olate with Propene through FTIRIn-Line Monitoring

Karin Sahre,* Ulrich Schulze, Klaus-J. Eichhorn, Brigitte Voit

The consumption of 10-undecene-1-olate (UOA) during its continuous re-feeding in the metal-locene-catalyzed copolymerizationwith propenewas investigated by ATR-FTIR spectroscopy in-line monitoring through evaluation of the integral absorbances of the characteristic IR bands.For the quantitative determination of the comonomer concentration during the copolymer-ization reaction with and without continuous re-feeding of UOA, multiple calibration func-tions based on the chemometric partial least squaresmethodwere applied. For the first time, adirect correlation between the consumption ofan olefin and the addition of a polar comono-mer during ametallocene-catalyzed copolymer-ization was demonstrated. By means of thistechnique, a relatively constant molar stoichio-metric ratio of the comonomer and propeneover the whole polymerization time wasachieved, which is very important in obtainingcopolymers with defined random structureand, thus, from the point of view of reactionengineering, constant product quality.

Introduction

The polar functionalization of poly(propylene) (PP) is

important in order to improve its surface properties for

several applications, for example, for achieving varnish-

able and gluable parts. By this functionalization, the

excellent mechanical properties of PP can be combined

with polar properties necessary for interactions with other

compounds. The challenge is, however, to synthesize

K. Sahre, U. Schulze, K-J. Eichhorn, B. VoitLeibniz Institute of Polymer Research Dresden, Hohe Straße 6,D-01069 Dresden, GermanyFax: þ49 351 465284; E-mail: [email protected]

Macromol. Mater. Eng. 2009, 294, 250–255

� 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

homogeneous propene copolymers with a constant con-

tent of a polar comonomer in every copolymer chain, since

the presence of polar groups usually strongly reduces the

activity of the insertion polymerization catalyst and the

polymerization reactivity of propene and the polar

comonomer differ significantly.

In recent years, the metallocene-catalyzed copolymer-

ization of propene with polar monomers has been

described, comprising the pre-reaction of the comonomer

with aluminum alkyls.[1–9] The corresponding reaction

pathway is demonstrated in Scheme 1. In our previous

work,[1] we focused on kinetic studies of this reaction using

in-line ATR-FTIR spectroscopy monitoring. Hackmann und

Rieger[10] have already discussed the synthesis of func-

DOI: 10.1002/mame.200800329

Defined Comonomer Re-Feeding During the Metallocene-Catalyzed Copolymerization of . . .

Scheme 1. Reaction pathways of the pre-reaction of the comonomer with aluminumalkyls and of the polymerization step using the catalyst system Et-Ind2/MAO.

tional propene copolymers with more uniform composi-

tion by using IR spectroscopy data to control the

comonomer concentration during the copolymerization.

However, in that copolymerization process the propene

was continuously re-feed but the liquid comonomer was

introduced in one batch before the start of the copolymer-

ization. Only if the consumed comonomer is also re-feed

can a uniform distribution of the comonomer units along

the PP backbone be expected.

The goal of our work is to obtain a copolymer of propene

and 10-undecene-1-ol (UO) or, more exactly, 10-undecene-

1-olate (UOA)with further reduced chemical heterogeneity

and more homogenous structural uniformity by contin-

uous re-feeding of both monomers. In this study, in-line

monitoring by ATR-FTIR spectroscopy will be demon-

strated as an appropriate method for the qualitative and

quantitative estimation of the comonomer UO consump-

tion in the copolymerization with propene. This knowl-

edge will allow a defined re-feeding of also the consumed

polar comonomers, besides the established continuous re-

feeding of propene during the metallocene-catalyzed

copolymerization, in order to keep a constant molar ratio

of both monomers throughout the polymerization.

Experimental Part

Materials

Toluene (Fluka, p.a.) was dried over sodium/potassium and

distilled prior to use. As inert gas argon 5.0 (Air Liquid) was used.

Propene (2.8 grade) was purchased from Riessner-Gase. It was

purified by R3-11 copper oxide catalysts (BASF) followed by

passing through 3 A molecular sieves. Asmetallocene catalyst rac-

Et[Ind]2ZrCl2 rac-ethylene bis-indenyl zirconium dichloride

(abbreviated as Et-Ind2; Crompton GmbH) was used as received.

Methylaluminoxane (MAO) solution and triisobutyl aluminum



(TIBA) (both from Crompton GmbH) were used

as obtained. The 10-undecene-1-ol (UO)

(Aldrich) was distilled and stored over a

molecular sieve before use in copolymerization.

Metallocene-Catalyzed

Copolymerization

The copolymerization experiment was carried

out in a 1 L stainless steel autoclave (Buchi) at

50�0.3 8C. The propene was constantly re-feed

by setting the total propene pressure to be

1.2 bar and the propene consumption was

monitored by a Pressflow gas controller (Buchi).

First, 200 mL toluene, 32 mL cocatalyst MAO

(10 wt.-% solution in toluene) and the solution

of UOA (pre-reacted UOwith TIBA)were poured

into the autoclave. Then, propene gas was

added. The copolymerization was initiated

by injecting 2.5 or 5 mL catalyst solution (cat; Et-Ind2 in toluene).

The catalyst concentration was 1.6�10�5 mol � L�1. The

comonomer concentration in the feed was varied from 265 to

325 (� 5) mmol � L�1. The temperature, propene pressure,

instantaneous gas flow and total propene consumption were

monitored and recorded as a function of time using a computer.

IR Monitoring

The metallocene-catalyzed copolymerization reaction was mon-

itored using a ReactIRTM 4000 in-line measuring system (Mettler-

Toledo) based on the well-known ATR technique.[1,2,11–16] For this,

a special diamond ATR probe (SentinelTM) was fixed at the bottom

of the autoclave. The probe was linked via mirror arms to an FTIR

spectrometer. Spectra were recorded continuously every minute

for a maximum of 3 h during the copolymerization. 55 scans were

co-added and averaged with a resolution of 2 cm�1 for each

spectrum.

Results and Discussion

In the copolymerization experiments of propene and UOA,

toluene, the cocatalyst MAO and the solution of UOA (pre-

reacted UOwith TIBA) were poured first into the autoclave

equipped with the ATR-IR spectroscopy probe and then a

defined amount of propene gas introduced on before the

polymerization was initiated by injection of the catalyst

concentration. The propene was constantly re-feed by

setting the total propene pressure to be 1.2 bar and the

propene consumption was monitored by a Pressflow gas

controller.

In all ATR-FTIR spectroscopy measurements, the spectra

of MAO, toluene and propene were included in the

background spectrum in order to eliminate their spectral

contributions. Because of the controlled constant concen-

tration of propene by continuous re-feeding during the

copolymerization, it was possible to remove its systematic

www.mme-journal.de 251

K. Sahre, U. Schulze, K.-J. Eichhorn, B. Voit

Figure 1. Profiles of the integral absorbances Aint of the doop ––CH2and n C––C bands of UOA during the metallocene-catalyzedcopolymerization without re-feeding.

252

spectral contributions from the bands of the double bond

of the comonomer as described previously by Hackmann

and Rieger.[10] Thus, the terminal out-of-plane vinyl

deformation vibrations doop ––CH2 and the stretching

vibrations n C––C can be used for the analysis of the

content of the comonomer UOA by the determination of

the profiles of their integral absorbances (integration

limits 929/896 and 1 647/1 626 cm�1) during the copoly-

merization. Due to its high change in intensity upon UOA

consumption, the doop ––CH2 band is ideally suited for the

determination of the comonomer content. In principle, the

stretching vibration n C––C can also be used, but its change

in intensity seems to be too low and inconsistent for a

reliable evaluation of the comonomer content.

At first, the copolymerization reaction was carried out

without re-feeding of the comonomer UOA and was

monitored on the basis of the profiles of the integral

characteristic absorbances of the comonomer double

bonds. Figure 1 shows the corresponding curves. As

expected, the comonomer content is continuously

decreased after adding the catalyst solution.[1] These

results are the base for the experiments with re-feeding

of comonomer because the calculated integral absorbances

are directly associated with the comonomer concentration

at every measurement point.

In the second step, the metallocene-catalyzed copoly-

merization was performed with re-feeding of the

comonomer UOA. For the permanent monitoring of the

concentration of the comonomer the integral absorbance

of the characteristic doopCH2 band was used. In Figure 2

the profile of the integral absorbance of that band during

the copolymerization reaction is shown, indicating the

points of addition of the catalyst and comonomer

Figure 2. Profiles of the integral absorbance Aint of the doop ––CH2 band (^) with stepwisere-feeding of comonomer solution and the corresponding propene consumption (�)during the copolymerization. Addition of catalyst solution: a¼ 5 mL. Addition of UOAcomonomer solution: A¼ 25, B¼ 10, C¼ 10, D¼ 10 mL.

solutions. It shows that the stepwise

re-feeding of the comonomer solution is

excellently reproduced in the FT-IR

spectroscopy experiment. Moreover, this

experiment shows for the first time the

direct correlation between the UOA

concentration and the propene con-

sumption during the copolymerization

process. After the addition of the UOA,

the propene conversion dropped to zero

according to a short-term reduction of

the catalyst activity. It has to be

assumed that the shield of the polar

groups is not complete, also due to pre-

treatment of the catalyst by TIBA.

Subsequently, the propene consumption

starts again and accelerates with UOA

conversion, since this leads to a reduc-

tion of the deactivating effect of UOA.

The polymerization rates of both com-

ponents decrease after each UOA re-


� 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/mame.200800329


Figure 3. Multivariate regression, PLS prediction of the concentration of UOA(R2 ¼0.995).

feeding step over the full period of

copolymerization, due to the repeated

deactivation of the catalyst. However,

we assume that the observed strong and

short-term increase of the propene con-

sumption (Figure 2) during the addition

of the UOA is a result of the sudden

increase of the toluene volume in the

reactor by injection of the toluene

containing UOA solution.

For the quantitative determination of

the comonomer concentration during the

copolymerization, reaction external cali-

bration functions were calculated using

the partial least squares (PLS) chemo-

metric regression method by evaluating

the measured spectra with the chemo-

metric software iC IRTM 3.0, Quant 1.0 (Mettler-Toledo

AutoChem).[17] Mixtures of known monomer concentra-

tions were measured as calibration standards by ATR-FTIR

spectroscopy at 50 8C under similar conditions as in the

copolymerization. The perturbing spectral influences on

the IR spectrum of the other components of the reaction

mixture – propene, MAO and TIBA – were eliminated by

the background spectrum.[1,2] The integral absorbances of

the characteristic IR spectral regions of UOA at 929–896,

1 648–1 627 cm�1 and of toluene as solvent at 1 615–1 590,

1 515–1 480 cm�1 were calculated and interlinked and the

different combinations yielded the calibration functions

with very similar results. That means several calibration

possibilities exist for determining the absolute concentra-

tion of UOA during the copolymerization. In Table 1, the

interlinked spectral regions used for the calibration are

demonstrated.

Table 1. Assignments of spectral regions to calibrations (Cal).

Calibration function Spectral region

cmS1

Cal 1 929–896

929–896

Cal 2 1615–1590

929–896

Cal 3 1515–1480

929–896

Cal 4 1648–1627

929–896

Cal 5 1615–1590

1648–1627



The results of using the chemometric regression for

evaluation of the calibration function Cal 5 to calculate the

comonomer concentration UOA are exemplified by

Figure 3. First the calibration functions were chosen for

determination of the comonomer concentration during the

copolymerization reaction without re-feeding of UOA. The

averaged initial concentration calculated using PLS

amounts to approximately 330� 10 mmol � L�1 (�3%)

and correlates excellently with the initial feed concentra-

tion of 325 mmol � L�1. Figure 4 shows that the changes of

comonomer concentration during the copolymerization

determined by the described calibrations (Cal 1–5) are

nearly the same. However, from the start to the finish of

the copolymerization reaction, the estimated percentage

error increases only up to about �7% at an average

concentration of 240 mmol � L�1. These good results allow

the multiple calibration functions created for the deter-

mination of the comonomer concentration to be used both

Figure 4. Dependence of comonomer concentration without re-feeding of UOA on polymerization time estimated by the severalcalibration functions at 50 8C (exemplary).


K. Sahre, U. Schulze, K.-J. Eichhorn, B. Voit

Table 2. Comparison of initial UOA concentrations in the feed and determined by calibration functions.

Experiment Initial feed concentration Percentage error

Actual Determined by calibration functions

mmol � LS1 mmol � LS1 %

1 265 260–270 –

Ø 265

2 270 260–270 2

Ø 265

3 270 270–280 1

Ø 273

4 300 300–310 2

Ø 305

5 275 258–265 5

Ø 261

6 275 250–265 7

Ø 257

7 280 285–300 4

Ø 290

254

with and without re-feeding of UOA solutions during the

metallocene-catalyzed copolymerization.

In the second and most important step, the calibration

functions were applied to quantify the UOA comonomer

concentration with re-feeding during the copolymeriza-

tion reaction in order to replenish accurately the consumed

amount of UOA for a homogenous distribution of the

comonomer units along the PP chains. For this challenge,

three calibrations were chosen and used for seven

experiments. The results are summarized in Table 2. It is

shown that the UOA concentrations determined by the

Figure 5. Dependence of comonomer concentration on polymer-ization time with re-feeding estimated by the several calibrationfunctions (Cal 2, 4, 5 as examples).



calibration functions are in good correlation with the

initial feed concentrations.

Figure 5 shows that different calibration functions can

be successfully applied for the estimation of the UOA

concentration during the copolymerization with UOA re-

feeding; for example, in Experiment 4 the initial feed

comonomer concentration was 300 mmol � L�1 and, by

means of the calibration functions, the calculated

initial concentration amounts were between 300 and

310 mmol � L�1 with an error of �4%.

Conclusion

The in-line monitoring of a metallocene-catalyzed copo-

lymerization reaction was carried out by ATR-FTIR

spectroscopy. The method used analyzes quantitatively

the consumption of the comonomer 10–undecene-1-olat

(UOA) in the copolymerization with propene. The aim was

to obtain a defined re-feeding of consumedUOA during the

copolymerization and to use that to maintain a constant

monomer/comonomer ratio over the whole polymeriza-

tion time.

The qualitative in-line FTIR spectroscopic analysis of the

changes in comonomer concentration during the metallo-

cene-catalyzed copolymerization succeeded on the basis of

the analysis of the double bonds of the comonomer UOA

by the determination of the profiles of their integral

absorbances (integration limits 929/896 and 1647/

DOI: 10.1002/mame.200800329


1 626 cm�1). In particular, the doop ––CH2 band is optimally

suitable for that interpretation. It was possible to monitor

selectively the stepwise re-feeding of the comonomer

UOA. For the quantitative determination of the UOA

concentration during the copolymerization reaction,

multiple calibration functions were created by means of

the chemometric method PLS; by this method, the real-

time evaluation of the UOA concentration succeeded. It

was shown that the multiple calibration functions were

appropriate and allowed successful quantification of

changes in the UOA concentration both with and without

re-feeding. In the experiment selected for the detailed

demonstration of the analytical method, the initial feed

concentration was 300 mmol � L�1. Using the spectroscopic

calibration data, this concentration was measured to be

between 300 and 310 mmol � L�1 with an error of about

�4%. These results demonstrate a very good adaptation of

the suggested calibration functions. In consequence, it was

possible to ensure that the actual comonomer concentra-

tion during the whole polymerization process is on

average in the proposed target range due to defined re-

feeding followed by in situ FT-IR spectroscopy.

As an additional interesting result, a direct correlation

between the consumption of an olefin and the addition of

a polar comonomer, in that case propene and 10-undecene-

1-ol, could be demonstrated for the metallocene-catalyzed

polymerization for the first time. As expected the

polymerization rate of the propene decreases after each

stepwise addition of UOA due to the gradual deactivation

of the catalyst.

By means of the described process-control technique, a

relative constant molar stoichiometric ratio of polar

comonomer and propene was achieved and, thus, more

homogeneous and structural uniformly copolymers were

obtained. The results of the influence of the accuracy of re-

feeding on the homogeneity of the chemical structure of



the copolymers will be discussed in detail in a separate

publication.

Received: November 10, 2008; Revised: January 19, 2009;Accepted: January 20, 2009; DOI: 10.1002/mame.200800329

Keywords: comonomer re-feeding; copolymerization; FT-IR; in-line monitoring; metallocene catalysts

[1] K. Sahre, U. Schulze, K.-J. Eichhorn, B. Voit, Macromol. Chem.Phys. 2007, 208, 1265.

[2] K. Sahre, U. Schulze, T. Hoffmann, M. Abd Elrehim, K.-J.Eichhorn, D. Pospiech, D. Fischer, B. Voit, J. Appl. Polym. Sci.2006, 101, 1374.

[3] U. Schulze, D. Pospiech, H. Komber, L. Haussler, D. Voigt, M.Eschner, Eur. Polym. J. 2008, 44, 694.

[4] R. A. Wendt, G. Fink, Macromol. Chem. Phys. 2002, 203, 1071.[5] R. Goretzki, G. Fink, Macromol. Chem. Phys. 1999, 200, 881.[6] P. Aaltonen, G. Fink, B. Lofgren, J. Seppala, Macromolecules

1996, 29, 5255.[7] K. Hakala, T. Helaja, B. Lofgren, J. Polym. Sci. 2000, A38,

1966.[8] J. M. Santos, M. R. Ribeiro, M. F. Portela, S. G. Pereira, T. G.

Nunes, A. Deffieux, Macromol. Chem. Phys. 2001, 202, 2195.[9] K. Radhakrishnan, S. Sivaram, Macromol. Rapid Commun.

1998, 19, 581.[10] M. Hackmann, B. Rieger, Macromolecules 2000, 33, 1524.[11] Mettler-Toledo AutoChem In: Manual ReactIR, 2008.[12] St. Roberge, M. A. Dube, J. Appl. Polym. Sci. 2007, 103, 46.[13] A. Tuchbreiter, J. Marquard, B. Kappler, J. Honerkamp, R.

Mulhaupt, Macromol. Symp. 2004, 213, 327.[14] B. Kappler, A. Tuchbreiter, D. Faller, P. Liebetraut, W. Horbelt,

J. Timmer, J. Honerkamp, R. Mulhaupt, Polymer 2003, 44,6179.

[15] J. R. Lizotte, T. E. Long, Macromol. Chem. Phys. 2004, 205, 692.[16] M. Allmendinger, M. Zintl, R. Eberhardt, G. A. Luinstra, F.

Molnar, B. Rieger, J. Organomet. Chem. 2004, 689, 971.[17] Mettler-Toledo AutoChem, iC IRTM3.0, Quant 1.0, 2008.


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