Mechanism of Emulsion Polymerization

Emulsion polymerization is one of the most important processes for the manufacture of polymers for rubbers, plastics, coatings, finishes, and adhesives. By the correct choice of comonomers, initiators, surfactants, and reaction conditions, a great variety of latex products are manufactured which meet many specific requirements in their applications. However, there is a great gap between this mostly empirically developed and sophisticated technology and our scientific understanding of it. The present paper presents a theory based on a single internally consistent model which predicts several experimentally available data of emulsion polymerization: the particle size, the conversion—time relationship, the dependence of particle size and molecular weight on conversion, and the influence of surfactant, of initiator and of monomer. This theory is based on extension of the assumptions first proposed by Smith and Ewart and Haward, and later modified by Stockmayer and O'Toole. It differs from these earlier theories in that the derived relationships are quantitative and contain no adjustable parameters. Also, the validity limits of the predictions are defined. The present form of the theory does not apply to all monomers, initiators, surfactants and reaction conditions commonly used in the practice of emulsion polymerization although its predictions are in good accord with experimental results obtained with model systems complying with the assumed conditions.