Oligoradicals, emulsion polymerization

The kinetics of inverse emulsion polymerization can be classified more or less arbitrarily into two subclasses according to the solubility of the initiator. Note that the solubility in water of oil-soluble initiators was found to be oihanced (up to a factor of 3) by the presence of monomo [23,28,29], making possible initiation by radical pairs formed in the aqueous dispersed phase. On the other hand, homogeneous nucleation mechanisms generating oligoradicals in the continuous phase can also be operative in inverse emulsions due to the maiginal solubility of acrylamide in organic media (1.6 wt% in isoparaffinic solvents and 2 wt% in toluene) [3]. 

In emulsifier-free (hereafter referred to as soap-free ) polymerizations, the polymerization is carried out in the same way as described above, except that no surfactant is used. Nucleation occurs by oligoradical precipitation into unstable nuclei which collide to form larger particles. Polymerization takes place mainly within these monomer-swoUen particles, and the particles grow in similar manner to conventional emulsion polymerization. 

CRP/LRP methods have been applied in miniemulsion polymerization as it offers some unique technical advantages over an emulsion polymerization and can be regarded as a simpli ed model of emulsion polymerization, in which, ideally, all monomer droplets (of 50-500 nm size) are nucleated by entering aqueous oligoradicals and become polymer particles, while no new particles are nucleated by homogeneous nucleation, thus leading to simpler kinetic behavior. 

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