synopsisI n emulsion polymerization, the Smith and Ewart theory gives about two or three times the number of polymer particles obtained by experiment. I n this paper, a reaction model is proposed which, from the standpoint of reactor design, can give an adequate explanation of the whole course of an emulsion polymerization of monomer highly insoluble in water. Among other things, the generating process of polymer particles is examined in detail. It is demonstrated experimentally that a new parameter proposed here, which represents the degree of difficulty of monomer initiation in micelles, is indispensable in explaining that process. Also confirmed is that monomer initiation takes place more easily in polymer particles than in micelles. According to the new model, the progress of polymerization, i.e., monomer conversion, the number of the polymer particles, and properties of polymer thus produced can be estimated with satisfactory accuracy. Furthermore, approximate equations are derived for easier estimation.

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The polymerization of styrene initiated by potassium peroxodisulfate was conducted at 50 "C in oil-in-water microemulsions using sodium lauryl sulfate and 1-pentanol as emulsifier and cosurfactant, respectively. Based on the experimental findings that both particle size and molecular weight of the polymers are almost independent of styrene conversion and the initial initiator concentration, a kinetic scheme of the microemulsion polymerization of styrene is proposed, which assumes that (1) particle nucleation occurs in monomer-swollen micelles and almost all the radicals in the water phase enter the monomerswollen micelles and finally initiate polymerization therein, ( 2 ) with negligible radical termination in the water phase and (3) with negligible radical entry into the preformed polymer particles, and accordingly, (4) all chain-stopping events in the active polymer particles are chain transfer reactions to monomer. Based on this kinetic scheme, a simple kinetic model is proposed, which can explain fairly well the progress of styrene microemulsion polymerization in the initial stage.

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SynopsisThe purpose of this paper is to clarify the effect of stirring on the course of emulsion polymerization of, for example, styrene. It establishes the existence of an optimum range of stirring speed and three important factors which must be considered in carrying out emulsion polymerization. (1) Stirring significantly affects the course of reaction in the presence of an imperfectly purified nitrogen atmosphere. Consequently, the number of polymer particles produced and the polymerization rate per particle will be affected. (2) At higher stirring speeds, polymer particles coagulate and coalesce. At lower stirring speeds, the reaction rate is controlled by the monomer transport rate from monomer droplets to the aqueous phase. (3) Stirring contributes to the reduction of the number of micelles because emulsifier molecules are adsorbed onto the surfaces of monomer droplets finely dispersed by the stirring. At low emulsifier concentrations near the critical micelle concentration, this effect cannot be neglected.