Gamma radiation-initiated polymerization of styrene at high pressure. III. Emulsion polymerization with anionic emulsifiers

Values calculated for the activation volume for chain propagation, ΔV, for the polymerization of styrene in emulsions under a variety of conditions agree closely with that previously obtained in pure styrene (ΔV = ?18.6 cm³ mol^?1). The rate of initiation of emulsion polymerization by radicals produced in the water phase was independent of pressure; therefore ΔV is zero. This differs from initiation in pure styrene which is slightly retarded by pressure (ΔV = 2.0 cm³ mol^?1). The activation energy for the reaction in emulsion, as in pure monomer, decreases slightly with pressure. Chain transfer to monomer occurs to a much greater extent in emulsions than in pure monomer under similar temperature and pressure conditions. Values for the dependence of the polymerization rate on the initiator (i.e., the irradiation dose rate) and emulsifier concentration are consistent with Smith–Ewart, Case II kinetics.