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POLYMER

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Polymers are made of basic units called mers

Poly mermany repeat unit

These are usually Hydrocarbons –where major

constituent atoms are Hydrogen and Carbon

C C C C C C

HHHHHH

HHHHHH

Polyethylene (PE)

repeat

unit

ClCl Cl

C C C C C C

HHH

HHHHHH

Polyvinyl chloride (PVC)

repeat

unit

HH

HHH H

Polypropylene (PP)

C C C C C C

CH3

HH

CH3CH3H

repeat

unit

POLYMER

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Ancient Polymer History

• Originally natural polymers were used

– Wood – Rubber

– Cotton – Wool

– Leather – Silk

• Some of the Biological Polymers

– Proteins, Enzymes, Cellulose

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Polymer Composition

Most polymers are hydrocarbons with covalent bond– i.e. made up of H and C

• Saturated hydrocarbons– Each carbon bonded to four other atoms

CnH2n+2

C C

H

H HH

HH

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Unsaturated Hydrocarbons

• Double & triple bonds relatively reactive – can form new bonds– Double bond – ethylene or ethene - CnH2n

• 4-bonds, but 3 atoms bound to C’s

– Triple bond – acetylene or ethyne - CnH2n-2

C C

H

H

H

H

C C HH

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Isomerism

– two compounds with same chemical formula can have

quite different arrangement

Ex: C4H10

• n-Butane

Iso-Butane

Boiling points -0.5 , -12.3 °C

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Chemistry of Polymers

Ethylene: C2H4

C C

H H

HH

monomer(ethylene)

R +

free radical

R C C

H

H

H

H

initiation

R C C

H

H

H

H

C C

H H

HH

+ R C C

H

H

H

H

C C

H H

H H

propagation

dimer

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Bulk or Commodity Polymers

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Synthesis of polymers

(Polymerization)

• Process of forming large molecules from

small molecules is Polymerization.

• Raw materials is from coal, natural gas,

petroleum products.

• Polymerization classified in to Addition and

condensation.

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Addition (Chain) Polymerization

– Initiation

– Propagation

– Termination

Monomers are attaching and form macro molecule.

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Condensation (Step) Polymerization

Involved more Monomers to form macro molecule.

Attain H2O byproduct.

Form cross link or network polymers.

Reaction time is longer.

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Molecular Shape

Conformation – Molecular shape can be

changed by rotation around the bonds

note: no bond breaking needed

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End to End Distance (r)

much smaller than the

chain length

Molecular chain have bends,

kinks, coils

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MOLECULAR WEIGHT

iiw

iin

MwM

MxM

Σ=

Σ=

Mw is more sensitive to higher

molecular weights

• Molecular weight, Mi: Mass of the chains.

Lower M higher M

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Molecular Weight Calculation

Example: average mass of a class

N i M i x i wi

# of students mass (lb)

1 100 0.1 0.054

1 120 0.1 0.065

2 140 0.2 0.151

3 180 0.3 0.290

2 220 0.2 0.237

1 380 0.1 0.204

10 1860 M n M w

186 lb 216 lb

∑=iiw MwM

∑=iin MxM

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Degree of Polymerization, n

n = number of repeat units per chain

unitrepeat ofweight molecular where

=

=

m

m

Mn

n

n

C C C C C C C CH

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

C C C C

H

H

H

H

H

H

H

H

H( ) ni = 6

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13.3) Number -average Molecular weight of Polystyrin is 500,000 g/mol. What is DP

Polystyrene is H8 C8

• Covalent chain configurations and strength:

Direction of increasing strengthDirection of increasing strengthDirection of increasing strengthDirection of increasing strength

POLYMER STRUCTURE

Branched Cross-Linked NetworkLinear

secondarybonding

Polyethylene, PVCVulcanized Rubber Phenol-formaldehyde

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Polymers – Molecular Configurations

Configurations – Arrangement of units along the axis

- to change must break bonds

• Stereoisomerism: Atoms link in the same order

C CR

HH

HC C

H

H

H

R

or C C

H

H

H

R

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Stereoisomerism

Tacticity – stereoregularity of chain

C C

H

H

H

R R

H

H

H

CC

R

H

H

H

CC

R

H

H

H

CC

C C

H

H

H

R

C C

H

H

H

R

C C

H

H

H

R R

H

H

H

CC

C C

H

H

H

R R

H

H

H

CC

R

H

H

H

CC

R

H

H

H

CC

isotactic – all R groups on same side

of chain

syndiotactic – R groups

alternate sides

atactic – R groups random

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Geometrical Isomerism

C CHCH3

CH2 CH2

C CCH3

CH2

CH2

H

cis-isoprene

(natural rubber)

CH3 & H groups on same

side of chain

trans-isoprene

CH3 & H groups on opposite

sides of chain

cistrans

Atoms link in the double bond

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Copolymers

two or more monomers polymerized together

• random – A and B randomly vary in chain

• alternating – A and B alternate in polymer chain

• block – large blocks of A alternate with large blocks of B

• graft – chains of B grafted on to A backbone

A – B –

random

block

graft

alternating

unitsmulty ofweight molecular Avrg where

=

=

m

m

MDP

n

*f where ∑= mjjm

13.17) Calculate the number-average molecular weight of a random

poly(Isobutylene-isoprene) copolymer in which the fraction of

Isobutylene repeat units are 0.25; assume that this concentration

corresponds to degree of polymerization of 1500

Isobutylene = C4 H8 isoprene = C5 H8

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Classification by temperature behavior

1) Thermoplastics 2) Thermosets

1) Synthesis is reversible and repeated.

By raising temp. secondary bonds diminished

Mostly Linear and Branched polymers

Eg: PVC, Polyethylene, Polystyrene etc

2) Network and covalent cross linked

Synthesis is non reversible.

By raising temp. degradation

Eg: Vulcanized rubber,

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Polymer CrystallinityEx: polyethylene unit cell

• Crystals must contain the

polymer chains in some way

– Chain folded structure

10 nm

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Polymer Crystallinity

Polymers rarely 100% crystalline

• Too difficult to get all those chains aligned

• % Crystallinity: % of material

that is crystalline.

-- TS and E often increase

with % crystallinity.

-- Annealing causes

crystalline regions

to grow. % crystallinity

increases.

crystalline

region

amorphous

region

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Polymer Crystal Forms• Single crystals – only if slow careful growth

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Polymer Crystal Forms

Spherulite

surface

• Spherulites – fast

growth – forms

lamellar (layered)

structures

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Spherulites – crossed polarizersMaltese cross

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13.6 Mn, Mw, Polymer (m) if DP = 477

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13. 8 High-density polyethylene may be chlorinated by inducing the

random substitution of chlorine atoms for hydrogen.

(a) Determine the concentration of Cl (in wt%) that must be added if this

substitution occurs for 8% of all the original hydrogen atoms.

(b) In what ways does this chlorinated polyethylene differ from polyvinyl

chloride?

B) 25% of the side-bonding sites are substituted with Cl, and

the substitution is probably much less random.

13.19 (a) Determine the ratio of butadiene to acrylonitrile repeat units

in a copolymer having a number average molecular weight of 250,000

g/mol and degree of polymerization of 4640.

(b) Which type(s) of copolymer(s) will this copolymer be, considering

the following possibilities: random, alternating, graft, and block? Why?

Butadiene = C4 H6 acrylonitrile = C3 H3N

B) the possibilities for this copolymer are random, graft, and block.

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�13.7 Is it possible to have homopolymer for PVC if DPpvc = 1120 ? Why ?

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