Emulsion copolymerization of acrylonitrile and butyl acrylate, 2. Effect of a radical scavenger on the rate of copolymerization and the copolymer composition

Random copolymers of acrylonitrile and butyl acrylate, covering two sets of compositions, are synthetized by emulsion copolymerization conducted to both low and high conversions. The copolymer formed at low conversion is enriched with acrylonitrile. Addition of a small amount of hydroquinone, however, suppresses the formation of copolymer enriched with acrylonitrile, i.e., the formation of copolymer more homogeneous in composition is favoured. Moreover, the effect of a radical scavenger on the kinetic parameters of the emulsion copolymerization is analyzed. In the presence of a small amount of hydroquinone the molecular weight of copolymer is somewhat increased when compared with that prepared without hydroquinone. In addition, the rate of copolymerization unexpectedly decreases with increasing emulsifier concentration. It is supposed that the recipe ingredients themselves and their reaction products or/and intermediates participate in termination reactions within the monomer swollen polymer particles and probably within the emulsified monomer droplets. The initiation of the emulsion copolymerization of acrylonitrile and butyl acrylate is a two-step process. The first step starts in the aqueous phase by the primary radicals from the water-soluble initiator and acrylonitrile. The second step occurs in the monomer-swollen emulsifier micelles by water-soluble and -insoluble radicals (primary and macroradicals) and by radicals derived from the recipe ingredients.