Emulsion polymerization mechanisms and kinetics

Emulsion polymerization involves the propagation reaction of free radicals with monomer molecules in a very large number of discrete polymer particles (1016-1018 dm−3) dispersed in the continuous aqueous phase. The nucleation and growth of latex particles control the colloidal and physical properties of latex products. This review article focused on the polymerization mechanisms and kinetics involved in such a heterogeneous polymerization system over the preceding 10-year period. First, an overview of the general features of emulsion polymerization was given, followed by the discussion of several techniques useful for studying the related polymerization mechanisms and kinetics. Emulsion polymerizations using different stabilizers were studied extensively in the last few years and representative publications were reviewed. The performance properties of some specialty polymerizable, degradable or polymeric surfactants and surface-active initiators were also evaluated in emulsion polymerization. At present, the particle nucleation process is still not well understood and deserves more research efforts. This article continued to discuss the origin of non-uniform latex particles from both the thermodynamic and kinetic points of view. This was followed by the discussion of various reaction parameters that had significant effects on the development of particle morphology. Recent studies on the polymerization in non-uniform polymer particles were then reviewed. Finally, the polymerization mechanisms, kinetics and colloidal stability involved in the versatile semibatch emulsion polymerization were reviewed extensively.