Efficiency of initiation by azodiisobutyronitrile in the emulsion polymerization of styrene

Abstract

Oil-soluble initiators can produce rates of emulsion polymerization similar to those obtained with the water-soluble initiators which are normally used. Although radicals are generated in pairs in the oil phase, escape of a radical to the aqueous phase leaves an isolated radical in the oil phase: this is the essential condition for an emulsion polymerization. A concentration of azodiisobutyronitrile was found which produced the same number of latex particles in the emulsion polymerization of styrene as was obtained with a typical concentration of potassium peroxydisulphate. The rate of nucleation of latex particles can then be equated to that obtained with the known rate of decomposition of peroxydisulphate. Comparison with the rate of decomposition of azodiisobutyronitrile shows its efficiency to be only 4% in emulsion polymerization in contrast with the efficiency of ∼50% obtained in bulk or solution polymerization.