Effects of surfactants on acrylonitrile polymerization initiated by a Cr(VI)–cyclohexanone redox system: A kinetic study

Abstract

ABSTRACT:The polymerization of acrylonitrile (AN) was kinetically studied with a Cr(VI)-cyclohexanone (CH) redox system as an initiator from 25 to 45°C in the presence of a surfactant. The rate of polymerization and the percentage of the monomer conversion increased as the concentration of the anionic surfactant [sodium dodecyl sulfate (SDS)] increased above its critical micelle concentration. However, the cationic surfactant (cetyltrimethylammonium bromide) reduced the rate considerably at higher concentrations, whereas the nonionic surfactant (TX-100) had no effect on the rate. The effects of the Cr(VI), CH, AN, and H ϩ concentrations and the ionic strength on the rates were also examined. The presence of 0.015M SDS reduced the overall activation energy of the polymerization by 5.55 kcal/mol with respect to that in the absence of the surfactant. With increasing SDS concentration, the viscosity-average molecular weight also increased. A suitable mechanistic scheme was proposed for the polymerization process.