REDOX POLYMERIZATION OF 2-HYDROXYETHYL METHACRYLATE (HEMA) .1. INFLUENCE OF SURFACTANTS ON POLYMERIZATION KINETICS

Oxidation of ferrous orthophenanthroline (FeP) by peroxydiphosphate (P P) in aqueous medium at pH 1. was followed spectrophotometrically. Kin etic analysis has shown that oxidation occurs via the formation of an intermediate complex between FeP and PP. Equi librium and rate constan ts were calculated. Influence of surfactants on the oxidation of FeP b y PP was also investigated. The equilibrium constant for complex forma tion was found to be higher in the presence of surfactants. The enhanc ed complex formation has been attributed to the ionic interactions bet ween the charged surfactant and the ionic species in the reaction medi um. Polymerization of HEMA initiated by the redox system, FeP/PP, was carried out in aqueous medium, under the conditions of excess reductan t over oxidant and excess oxidant over reductant. The polymerization f ollowed different mechanisms under these conditions; with excess oxida nt, the growing polymer radicals underwent oxidative termination, whil e with excess reductant, primary radical termination was preferred. Th e effect of surfactants on the aqueous polymerization of HEMA using th e redox system FeP/PP was also investigated. In addition to the decrea se in rate, the polymerization followed a different mechanism in the p resence of surfactants, the growing radicals terminated by mutual inte raction. (C) 1995 John Wiley & Sons, Inc.