Polymer SynthesisCHEM 421

• Odian Book

Chapter 6-2

Polymer SynthesisCHEM 421

Copolymers

• Copolymers involve the use of two or more monomers

• Copolymers allow us to tailor product properties

– Tg

– Tm

• Commercially important (chain growth) examples include:

– Styrenics

» Styrene/acrylonitrile (SAN): increased impact resistance and solvent resistance; 10-40% AN, Samsonite luggage

» Styrene/butadiene (SBR): 25% styrene/75% butadiene

» Largest volume synthetic rubber (tires)

» HIPS: High Impact PS (PBD-g-PS)

» Styrene Maleic Anhydride (SMA)

Polymer SynthesisCHEM 421

Copolymers

• Commercially important copolymers (Cont’d)

–Vinyl chloride

» Rigid PVC: ca. 5% vinyl acetate, lowers Tg small amount allow to be processed a lower temperatures avoiding degradation

» Flexible: 20-40% vinyl acetate (tubing, sheets (e.g. shower curtains, etc.)

» Packaging: Saran Wrap® (90% vinylidene chloride)

Polymer SynthesisCHEM 421

Copolymers

• Commercially important copolymers (Cont’d)

– Ethylene (> 10 billion lbs/yr)

» LDPE (homopolymer!)

» High pressure free radical

» 30-40% x-tallinity

» HDPE (homopolymer!)

» Ziegler-Natta

» 75% x-tallinity

» Linear Low Density Polyethylene

» Linear copolymer with 1-5 mol% α-olefins

» EVA: Ethylene vinyl acetate: 2-40% vinyl acetate

» Packaging, molding

» EPR: Ethylene-propylene rubber (plus cure site monomer)

» Ethylene/acrylic acid: (1-10 mol% AA); ionomer

» Surlyn®

Polymer SynthesisCHEM 421

Copolymers

• Commercially important copolymers (Cont’d)

–Fluoropolymers

» PTFE: Tm = 335 °C, Tg = -70 °C

» PVDF: Tm = 180 °C

» FEP: Tm = 250 - 280 °C, Tg = 70 - 120 °C

» ETFE: Tm = 225 °C, Tg = 145 °C

» PFA: Tm = 300 °C

» Teflon AF:

» Nafion:

Polymer SynthesisCHEM 421

Copolymerization Kinetics

M1 + M1 M1M1

k11

M1 + M2 M1M2

k12

Homo-propagation

Cross-propagation

Terminal Model

Polymer SynthesisCHEM 421

Copolymerization Kinetics

M1M1 + M1 M1M1M1

k111

Penultimate Model

M2M1 + M1 M2M1M1

k211

….

.

Polymer SynthesisCHEM 421

Copolymerization Kinetics

M1 + M1 M1M1

k11

M1 + M2 M1M2

k12

M2 + M1 M2M1

k21

M2 + M2 M2M2

k22

Homo-propagation

Cross-propagation

Cross-propagation

Homo-propagation

Terminal Model

Polymer SynthesisCHEM 421

Copolymerization Kinetics

M1 + M1 M1M1

k11

M1 + M2 M1M2

k12

M2 + M1 M2M1

k21

M2 + M2 M2M2

k22

Rp11 = k11 [M1•] [M1]

Terminal Model

Rp12 = k12 [M1•] [M2]

Rp21 = k21 [M2•] [M1]

Rp22 = k22 [M2•] [M2]

Polymer SynthesisCHEM 421

Copolymerization Kinetics

- ——— = k11 [M1•] [M1] + k21 [M2•] [M1]d [M1]

dt

- ——— = k12 [M1•] [M2] + k22 [M2•] [M2]d [M2]

dt

The rate of disappearance of M1 and M2 can be expressed as:

Polymer SynthesisCHEM 421

Copolymerization Kinetics

d [M1] k11 [M1•] [M1] + k21 [M2•] [M1]

d [M2] k12 [M1•] [M2] + k22 [M2•] [M2] ——— = ——————————

The ratio of the two rates is then:

d [M1] [M1] k11 [M1•] + k21 [M2•]

d [M2] [M2] k12 [M1•] + k22 [M2•] ——— = ——— ——————————

Simplify:

Polymer SynthesisCHEM 421

Copolymerization Kinetics

Assume the Steady State Approximation:

The concentrations of M1• and M2• are constant Therefore:

The rate of addition of M1• to M2 will equal The rate of addition of M2• to M1

k11 k22

k12 k21

r1 = ——— r2 = ———

Define:

k12 [M1•] [M2] = k21 [M2•] [M1]

Polymer SynthesisCHEM 421

Copolymerization Kinetics

Copolymer Composition Equation:

d [M1] [M1] r1 [M1] + [M2]

d [M2] [M2] [M1] + r2 [M2] ——— = ——— ———————

Molar ratio of the monomers in the

copolymer

Concentrations of the monomers in the

feed

Concentrations of the monomers in the

feed

Concentrations of the monomers in the

feed

Concentrations of the monomers in the

feed

Concentrations of the monomers in the

feed

Concentrations of the monomers in the

feed

Polymer SynthesisCHEM 421

Copolymerization Kinetics

Copolymer Composition Equation:

[M1]

[M1] + [M2]f1 = 1 – f2 = —————

d[M1]

d[M1] + d[M2]F1 = 1 – F2 = ———————

r1 f12 + f1 f2

r1 f12 + 2 f1 f2 + r2 f2

2 F1 = ——————————

Polymer SynthesisCHEM 421

Copolymerization Examples

• r1 = r2 = 1.0

–Monomers exhibit no preference for homo-propagation vs cross-propagation

–Truly random copolymer results

–F1 = f1

–Ethylene / vinyl acetate

0.0 0.2 0.4 0.6 0.8 1.0

1.0

0.8

0.6

0.4

0.2

0.0

F1

f1

A

Polymer SynthesisCHEM 421

Copolymerization Examples

• r1 = r2 = 1.0

• r1 = r2 = 0.0

–Monomers exhibit tendency to cross-propagate

–Alternating copolymer results

–F1 = 0.5

–Styrene / maleicanhydride

–TFE / ethylene

–1-Butene / sulfur dioxide

0.0 0.2 0.4 0.6 0.8 1.0

1.0

0.8

0.6

0.4

0.2

0.0

F1

f1

A

B

Polymer SynthesisCHEM 421

Copolymerization Examples

• r1 = r2 = 1.0

• r1 = r2 = 0.0

• r1 and r2 between 0 and 1.0

–Common

–Cross-over point

» Azeotropic polymerization

0.0 0.2 0.4 0.6 0.8 1.0

1.0

0.8

0.6

0.4

0.2

0.0

F1

f1

A

BC

Polymer SynthesisCHEM 421

Copolymerization Examples

• r1 = r2 = 1.0

• r1 = r2 = 0.0

• r1 and r2 between 0 and 1.0

• r1 >> 1.0 and r2 << 1.0

–Significant drift in feed ratio

0.0 0.2 0.4 0.6 0.8 1.0

1.0

0.8

0.6

0.4

0.2

0.0

F1

f1

A

BC

D