An investigation of emulsion polymerization using oil-soluble initiators



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The emulsion polymerization of styrene and methyl methacrylate using two oil-soluble initiators has been investigated. The thermal decomposition of tert-butyl peroxy-pivalate and the photolytic decomposition of di-tert-butyl peroxide in a styrene emulsion system have rates of polymerization which are comparable to the rates of polymerization of a styrene emulsion using the water-soluble initiator, potassium persulfate. The resulting polystyrene emulsions were found to polymerize to higher conversions with increases in molecular weight when additional charges of styrene were added. The increases in molecular weight were evidenced by increases in viscosity and gel permeation chromatography. Block copolymers of styrene, methyl methacrylate and acrylonitrile polymer radicals were prepared by delaying the addition of the blocking monomer until the initial monomer charge was quantitatively converted to polymer. The presence of initiator radicals stabilized by the surfactant has been proposed to explain the presence of homopolymers of the blocking monomer even after a delay which should have been sufficient for essentially complete initiator decay.