Inverse-emulsion polymerization of acrylamide using block copolymeric surfactants: mechanism, kinetics and modelling

Abstract

A comprehensive experimental investigation of the inverse-emulsion polymerization of acrylamide was carried out using an oil soluble initiator and a block copolymeric surfactant whose hydrophobic moiety is poly(12-hydroxystearic acid) and whose hydrophilic moiety is polyethylene oxide. It was found that the initial polymerization rate was first order with respect to molar monomer concentration, first order with respect to molar initiator concentration, and zeroth order with respect to molar emulsifier concentration. Based on these experimental findings, a mechanism was proposed which includes initiation, propagation, transfer to monomer and termination. The elementary reaction scheme also includes transfer to impurities which are found in the surfactant. The kinetic model developed from the proposed mechanism is found to be in good agreement with the experimental conversion and weight-average molecular weight data. Compared with sorbitan esters of fatty acids, the copolymeric surfactant provides higher polymerization rates and very high and linear molecular weights. These are comparable to those obtained by solution polymerization, however the total monomer level in the recipe can be substantially greater. Furthermore, stable inverse-laticies can be produced at emulsifier levels as low as 2 wt%.