EMULSIFIER-FREE EMULSION POLYMERIZATION WITH IONIC COMONOMER

Emulsion polymerization of styrene in the absence of emulsifier with K//2S//2O//8 as initiator produced uniform latices. Incorporation of ca. 0. 5% ionic comonomer (sodium styrenesulfonate) reduced the particle size from the range 0. 5-1. 0 mu m achieved in prior emulsifier-free formulations to a range of 0. 15-0. 40 mu m. Some advantages achieved by incorporation of ionic comonomer were higher polymer content and independently controllable surface charge density. Particle diameter varied as the 0. 64 power of the ratio of ionic strength to comonomer, as the minus 0. 20 power of initiator concentration, and as the 0. 46 power of monomer content. Kinetic data suggest that copolymerization takes place in the aqueous phase, and that nuclei for particle growth are formed by precipitation of the initially water-soluble copolymer. The latex is stabilized by sulfonic acid groups of the comonomer, as well as by sulfate end groups from the initiator.