polymer synthesis chem 421 odian book chapter 6-2
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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