Basic Principles ofEmulsion Polymerization

Dr. Nagendra KalvaNCL-PUNE 03/08/2016

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.

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.

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

Surfactant +Monomer

Monomer droplet

Initiator

Emulsion Polymerization mechanism:

1) Monomers

2) Dispersion medium

3) Emulsifier

4) Water soluble initiator.

Stage -I

Polymer latex

Diffusion of monomer from monomer droplet to the micelle

Complete disappearance of monomer droplets.

Stage -II Stage -III

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.

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.

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.

Micro emulsion Polymerization:

Polymerization occurs in small droplets size 10-100nm compared to 1-100m

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 1-100m

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.