EMULSIFIER-FREE EMULSION COPOLYMERIZATION OF STYRENE AND SODIUM STYRENE SULFONATE

The kinetics of the emulsifier-free emulsion copolymerization of styrene and sodium styrene sulfonate have been examined over a range of comonomer compositions. The rate of polymerization was found to increase dramatically in the presence of small amounts of sodium styrene sulfonate. This increase is attributed to the increased number of particles formed when sodium styrene sulfonate was present and to a gel effect enhanced by ion association. At low concentrations of functional comonomer, where a monodisperse product was obtained, a homogeneous nucleation mechanism of particle generation is proposed. At higher concentrations, broader and then bimodal size distributions were obtained, and this is ascribed to significant aqueous phase polymerization of sodium styrene sulfonate. The water-soluble homopolymer is supposed to act as a locus of polymerization. The occurrence of this aqueous phase side reaction and the generation of secondary particles makes impossible the preparation of highly sulfonated polystyrene latexes by batch or seeded batch emulsion copolymerization.