1. Odian Book: Chapter 4

2. 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. Emulsion Polymerization Recipe
Water (continuous phase)
Water-insoluble monomer
Water-soluble initiator
Surfactant (detergent)

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

5. Surfactants
Types
- Anionic
- Cationic
- Amphoterics
- Non-ionics

6. Emulsion Polymerization Recipe

7. Emulsion Polymerizations
Polym’z
Rate
Critical Micelle Concentration
Surfactant Concentration

8. Kinetics of Emulsion Polymerization
III
Percent
Conversion II I
Time

9. Kinetics of Emulsion Polymerization
Rate I II
III
% Conversion

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

11. Interval One: 0 – 15 % ConversionM M M I
I • I
Inactive
latex particles
Inactive
latex particles
Active
latex particle
Active
latex particles M I P• M M I M M M M M I
Micelles
Containing
Monomer
Micelles
Containing
Monomer
Micelles
Containing
Monomer M M P•
I • I M M I

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

13. Interval Two: 15 – 80% ConversionP•
Active
latex particles
Active
latex particles
Active
latex particles M M M I
I • I I M
I •
Number of particles constant, therefore
Rp = constant M
I • I M P• I P•
Inactive
latex particles
Inactive
latex particles
Inactive
latex particles I M M
No micelles M P• M I M I

14. Kinetics of Emulsion PolymerizationII
III
1018
1015
Number of
Polymer
Particles
Number of
Micelles
Time

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

16. Interval Three: 80 – 100% ConversionP• P•
No monomer droplets M M M I
I • I
I • M I M P• P• M P• I
I • M M
No micelles M M P• I M I

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

18. 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!

19. 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. Emulsion Polymerization Kinetics
How to increase Rp?
Increase N’ to increase rate
Increase surfactant concentration to increase N’

21. 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? rp Ri
= —— N ri
= —— DP
= kp[M] rp ri
N kp [M] Ri
= ——— DP

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