EMULSION POLYMERIZATION IN A HYBRID CARBON-DIOXIDE AQUEOUS-MEDIUM

The development of a new reaction medium is reported, based on a bipha sic mixture of carbon dioxide and water for emulsion polymerizations: a surfactant-free aqueous emulsion polymerization of methyl methacryla te using potassium persulfate under a varying head pressure of CO2 (0- 350 bar) at 75 degrees C. The resulting polymer is a stable latex with . particles of submicron size. The Effect of CO2 on polymerization is relatively small, until there is a significant change at high CO2 pres sure. This is seen by examining the molecular weight distribution in t he form of the log(number distribution), P(M) (readily obtained by GPC ). At pressures of 140 bar and below, the P(I) show the form expected for chain-stopping events dominated by transfer and by diffusion-contr olled termination. At 280 bar, In P(M) is significantly steeper than i ts lower-pressure counterpart at relatively low conversion(45%). This is attributed to swelling by supercritical CO2 reducing the viscosity of the particles, allowing more rapid termination.