Molecular weight distributions in terpolymerization of alpha-methylstyrene/styrene/acrylic acid in continuous stirred tank reactor

Free-radical terpolymerization of alpha -methylstyrene/styrene/acrylic acid (AMS/ST/AA) in a continuous stirred tank reactor (CSTR) was studied theore tically and experimentally. A series of reactions were conducted to investi gate the effect of the reaction temperature, residence time, solvent conten ts, initiator concentration, chain-transfer agent level, and different mono mer compositions on the molecular weight distribution (MWD). The mathematic al model based on "the instantaneous property method (IPM)" and the pseudok inetic rate constant method was introduced and modified to predict the MWD of the bulk terpolymer produced in a CSTR. The effects of process variables were included in the mathematical model. Extensive comparisons were made b etween the theoretical results and experimental values. The rate of the fre e-radical terpolymerization of AMS/ST/AA was comparatively slow and it was found that the concentration of cr-methylstyrene had a strong influence on the molecular weight and polydispersity of the MWD. This presumably reflect ed the existence of a normal bimolecular termination rate and a slow propag ation rate due to steric hindrances at the doubly substituted vinyl carbon atom or transfer of the allylic hydrogen from the ct-methyl group. Good agr eement was obtained between calculated MWD and the experimental one by assu ming that the disproportionation termination of free radicals was the domin ant chain-stoppage mechanism. (C) 2000 John Wiley & Sons, Inc.