1. Odian Book
Chapter 6-2

2. 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)

3. 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: % vinyl acetate (tubing, sheets (e.g. shower curtains, etc.)
Packaging: Saran Wrap® (90% vinylidene chloride)

4. 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®

5. Copolymers Commercially important copolymers (Cont’d) Fluoropolymers
PTFE: Tm = 335 °C, Tg = -70 °C
PVDF: Tm = 180 °C
FEP: Tm = °C, Tg = °C
ETFE: Tm = 225 °C, Tg = 145 °C
PFA: Tm = 300 °C
Teflon AF:
Nafion:

6. Copolymerization Kinetics
Homo-propagation
Cross-propagation
Terminal Model

7. Copolymerization Kinetics
…..
Penultimate Model

8. Copolymerization Kinetics
Homo-propagation
Cross-propagation
Cross-propagation
Homo-propagation
Terminal Model

9. Copolymerization Kinetics
Rp11 = k11 [M1•] [M1]
Rp12 = k12 [M1•] [M2]
Rp21 = k21 [M2•] [M1]
Rp22 = k22 [M2•] [M2]
Terminal Model

10. Copolymerization Kinetics
The rate of disappearance of M1 and M2 can be expressed as:
- ——— = k11 [M1•] [M1] + k21 [M2•] [M1]
d [M1] dt
- ——— = k12 [M1•] [M2] + k22 [M2•] [M2]
d [M2] dt

11. Copolymerization Kinetics
The ratio of the two rates is then:
d [M1] k11 [M1•] [M1] + k21 [M2•] [M1]
d [M2] k12 [M1•] [M2] + k22 [M2•] [M2]
——— = ——————————
d [M1] [M1] k11 [M1•] + k21 [M2•]
d [M2] [M2] k12 [M1•] + k22 [M2•]
——— = ——— ——————————
Simplify:

12. 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
k12 [M1•] [M2] = k21 [M2•] [M1]
Define:
k k22
k k21
r1 = ——— r2 = ———

13. 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

14. Copolymerization Kinetics
Copolymer Composition Equation:
[M1]
[M1] + [M2]
f1 = 1 – f2 = —————
d[M1]
d[M1] + d[M2]
F1 = 1 – F2 = ———————
r1 f f1 f2
r1 f f1 f2 + r2 f22
F1 = ——————————

15. 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
1.0
0.8
0.6
0.4
0.2
0.0 F1 f1 A

16. Copolymerization Examples
r1 = r2 = 1.0
r1 = r2 = 0.0
Monomers exhibit tendency to cross-propagate
Alternating copolymer results
F1 = 0.5
Styrene / maleic anhydride
TFE / ethylene
1-Butene / sulfur dioxide
1.0
0.8
0.6
0.4
0.2
0.0 F1 f1 A B

17. Copolymerization Examples
r1 = r2 = 1.0
r1 = r2 = 0.0
r1 and r2 between 0 and 1.0
Common
Cross-over point
Azeotropic polymerization
1.0
0.8
0.6
0.4
0.2
0.0 F1 f1 A B C

18. 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
1.0
0.8
0.6
0.4
0.2
0.0 F1 f1 A D B C