Emulsion polymerization involves radical chain polymerization where monomers are dispersed as droplets in water and polymerize within micelles. It allows for high molecular weight polymers to form at high reaction rates. The process involves four main components: 1) monomers, 2) a dispersion medium (water), 3) an emulsifier, and 4) a water-soluble initiator. Polymerization occurs only within the micelles. The mechanism proceeds in three stages: initiation within the micelles, monomer diffusion into particles as conversion increases, and consumption of monomer droplets. Emulsion polymerization produces polymer latex particles and addresses heat transfer and viscosity issues relative to other polymerization methods.

1. Basic Principles of
Emulsion Polymerization
Dr. Nagendra Kalva
NCL-PUNE 03/08/2016

2. Bulk Polymerization:
 Absence of any solvent
 Simple formulations, rapid reaction, pure polymer.
 Used in step-growth and chain growth polymerizations.
 Heat buildup, difficult to control and high viscosity.
Solution Polymerization:
 presence of solvent, effective heat dissipation.
 Easier to stir the polymer solution.
 Low rate of polymerization, low M.wt. polymers, Solvent recovery from viscous
polymer solution.

3. Suspension Polymerization:
 Monomer dispersed in a solution (usually water). Low viscosity.
Monomer droplets stabilized by the stabilizers (PVA, methyl cellulose).
Monomer soluble initiator is added to initiate the polymerization.
Heat dispersed efficiently by the water. Polymer obtains as granules.
Difficult in removal of additives.

4. Emulsion Polymerization:
 Radical chain polymerization,
 Polymerization of monomers occurs in the form of emulsion.
 Resemblance of suspension polymerization.
 Differs in the size of particles in which polymerization occurs and initiator.
 First introduced in the world war II.
Thermal and viscosity problems are less significant.
 Major difference between emulsion and other polymerization is to get high M.wt.
polymers with high reaction rates.
 Styrene –co-1,3 butadiene synthesized by the emulsion polymerization

5.  Emulsion Polymerization mechanism:
1) Monomers
2) Dispersion medium
3) Emulsifier
4) Water soluble initiator.
Stage -I

6. Polymer latex
 Diffusion of monomer from monomer droplet to the micelle
 Complete disappearance of monomer droplets.
Stage -II Stage -III

7.  The monomers dispersed in water as monomer droplets and stabilized by the
emulsifier.
 Emulsifier added to the solution above its CMC.
 Micelles size ranges from 2-10 nm.
 Each micelle consists of 50-150 surfactant molecules. Size of droplets depend on the
rotation speed.
Site of Polymerization:
 Water soluble initiator initiates the polymerization.
Polymerization occurs only in the micelles due to their large oil-water
Interfacial area.
Absence of polymerization is experimentally proved and this distinguish between
suspension and emulsion polymerization techniques.

8. Stage-1:
 Water soluble initiator starts the polymerization in the micelles and grows its size to
tens of nanometers (0.4 m).
 Each micelles become polymer particle.
 initiation also occurs in the aqueous solution but results oligomers due to the less
concentration of monomer in aqueous solution.
Stage-II:
 After 15% conversion the micelles are exhausted with monomer and new particle are
generated.
 The monomer diffuses from the monomer droplets to maintain thermodynamic
equilibrium between monomer and polymer.
Smith-Evart model
 After nucleation monomer micelles transforms to polymer particles.

9. Stage-III:
 After 40-60% conversion the monomer droplets are disappears from solution.
 Polymer particles remains constant both in number and diameter.
Initiators:
 Potasium or Ammonium persulfate, hydrogen peroxide, 2,2’-azobis(2-
amidinopropane) dihydrochloride.
 Should be water soluble.

10. Micro emulsion Polymerization:
 Polymerization occurs in small droplets size 10-100nm compared to 1-100m
 Excess amount of emulsifier used in these polymerization
 Capturing the radicals by the micelles happens through out the process
 Small latex particles <50nm are obtained from micro emulsion polymerization.
Mini emulsion Polymerization:
 Polymerization occurs in small monomer droplets size 50-1000nm compared to 1-
100m
 Emulsion stabilized by the “co-surfactant” such as cetyl alcohol and hexadecane.
 Long chain co-surfactant penetrate less in oil-water interface.
 Mini emulsions are usually stable for seversl days.