1. Polymer Synthesis
CHEM 421
Odian Book: Chapter 4

2. Polymer Synthesis
CHEM 421
Emulsion Polymerizations
• Economically important
• Western countries 108
tons/year
• 30% of all polymers made by free radical
methods
–emulsion polymers accounts for 40-50% of
this
• First employed during WWII for
production of synthetic rubber
• Today: MMA, VC, vinylidene chloride,
styrene, fluoropolymers, vinyl acetate,
EVA, SA, SBR, chloroprene, etc

3. Polymer Synthesis
CHEM 421
Emulsion Polymerization
Recipe
• Water (continuous phase)
• Water-insoluble monomer
• Water-soluble initiator
• Surfactant (detergent)

4. Polymer Synthesis
CHEM 421
Surfactants
H2O
Hydrophobic /
Lipophilic core
Surfactant
Concentration
Unimers Micelles
Critical Micelle
Concentration
(CMC)

5. Polymer Synthesis
CHEM 421
Surfactants
Types
- Anionic
- Cationic
- Amphoterics
- Non-ionics

6. Polymer Synthesis
CHEM 421
Emulsion Polymerization Recipe

7. Polymer Synthesis
CHEM 421
Emulsion Polymerizations
Polym’z
Rate
Surfactant Concentration
Critical Micelle Concentration

8. Polymer Synthesis
CHEM 421
Kinetics of Emulsion
Polymerization
Percent
Conversion
Time
I
II
III

9. Polymer Synthesis
CHEM 421
Kinetics of Emulsion
Polymerization
Rate
% Conversion
I II III

10. Polymer Synthesis
CHEM 421
Before Initiation
I
I
I
I
I
I
I I
I
M
M
M
M
M
M
M
M
M M
MM
M
M
M
M
M
M
M
Monomer Droplet
ca. 1 micron diameter
conc = 1011
/mL
stabilized by soap
Micelle Containing
Monomer
ca. 75 Å diameter
conc = 1018
/mL
Relative surface area
1 : 560
Initiation of micelles
statistically favored

11. Polymer Synthesis
CHEM 421
Interval One:
0 – 15 % Conversion
I •
I
I
I
I
I
I • I
I
M
M
M
M
M
M M
M
M
M
MM
M
PP••
PP••
M M
Micelles
Containing
Monomer
Active
latex particle
Micelles
Containing
Monomer
Micelles
Containing
Monomer
Active
latex particles
Inactive
latex particles
Inactive
latex particles

12. Polymer Synthesis
CHEM 421
Qualitative Details
Conversion Micelles Monomer
Droplets
Particle
Number
Particle
Size
Comments
I
0 – 15% present present increases increases
Nucleation
period,
Increasing
Rp
II
III

13. Polymer Synthesis
CHEM 421
Interval Two:
15 – 80% Conversion
I
I
I
I
I • I
I
M
M
M
M
M
M
MM
M
PP••
PP•• I •
I
M
M
PP••
Inactive
latex particles
Inactive
latex particles
Inactive
latex particles
Active
latex particles
Active
latex particles
I •
I
M
PP••
Active
latex particles
No
micelles
Number of
particles
constant,
therefore
Rp = constant

14. Polymer Synthesis
CHEM 421
Kinetics of Emulsion
Polymerization
Number of
Micelles
Time
I II III
Number of
Polymer
Particles
1018
0
1015
0

15. Polymer Synthesis
CHEM 421
Qualitative Details
Conversion Micelles Monomer
Droplets
Particle
Number
Particle
Size
Comments
I
0 – 15% present present increases increases
Nucleation
period,
Increasing
Rp
II
15 – 80% absent present constant increases
Constant #
of particles,
Cp =
constant
III

16. Polymer Synthesis
CHEM 421
Interval Three:
80 – 100% Conversion
I
I
I
I
I • I
M
M
M
M
M
M
M
PP••
PP••
I
M
M
PP••
I •
M
PP••
M
PP••
M
PP••
I •
No
monomer
droplets
No
micelles

17. Polymer Synthesis
CHEM 421
Qualitative Details
Conversion Micelles Monomer
Droplets
Particle
Number
Particle
Size
Comments
I
0 – 15% present present increases increases
Nucleation
period,
Increasing
Rp
II
15 – 80% absent present constant increases
Constant #
of particles,
Cp =
constant
III
80 – 100% absent absent constant roughly
constant
Constant #
of particles,
Cp =
decreasing

18. Polymer Synthesis
CHEM 421
Emulsion Polymerization Kinetics
• Once inside a particle, radical propagates
as rp = kp[M]
• Overall rate: Rp = kp[M][P.
]
• [P.
] = N’ñ (where N’ = the sum of micelle
and particle concentrations and
ñ = average # of radicals per particle)
• Therefore,
–Increase N’ to increase rate!
][' MknNR pp =

19. Polymer Synthesis
CHEM 421
Emulsion Kinetics, cont.
• Smith-Ewart Kinetics:
–Case 2: ñ = 0.5 (MOST CASES!)
» 1 radical per particle
» Half of the particles active, half not active
–Case 1: ñ<0.5
» Radical can diffuse out of the particle
» Monomer with higher water solubility
–Case 3: ñ>0.5
» Termination constant is low
» High viscosity, initiator; large particles

20. Polymer Synthesis
CHEM 421
Emulsion Polymerization Kinetics
• How to increase Rp?
–Increase N’ to increase rate
»Increase surfactant concentration to increase N’
][' MknNR pp =

21. Polymer Synthesis
CHEM 421
Molecular Weight in Emulsion
Polymerizations
• Molecular weight determined by rate of growth
of a chain divided by rate of radical entry (ri)
–How to increase molecular weight?
DP
rp
= ——ri
Ri
= ——
N
ri = kp[M]rp
N kp [M]
Ri
= ———DP

22. Polymer Synthesis
CHEM 421
Free Radical Solution
Polymerizations
• Recall
– To increase molecular weight…
» Increase monomer concentration
» Decrease initiator concentration
– To increase Rate of Polymerization
» Increase monomer concentration
» Increase initiator concentration
٧ =
kp [M]
2 (kt kd f [I])1/2
= —————
Can’t do
both!
Rp = kp [M] (kd f [I] / kt)1/2