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

Free-radical terpolymerization of α-methylstyrene/styrene/acrylic acid (AMS/ST/AA) in a continuous stirred tank reactor (CSTR) was studied theoretically and experimentally. A series of reactions were conducted to investigate the effect of the reaction temperature, residence time, solvent contents, initiator concentration, chain-transfer agent level, and different monomer compositions on the molecular weight distribution (MWD). The mathematical model based on 'the instantaneous property method (IPM)' and the pseudokinetic 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 between the theoretical results and experimental values. The rate of the free-radical terpolymerization of AMS/ST/AA was comparatively slow and it was found that the concentration of α-methylstyrene had a strong influence on the molecular weight and polydispersity of the MWD. This presumably reflected the existence of a normal bimolecular termination rate and a slow propagation rate due to steric hindrances at the doubly substituted vinyl carbon atom or transfer of the allylic hydrogen from the α-methyl group. Good agreement was obtained between calculated MWD and the experimental one by assuming that the disproportionation termination of free radicals was the dominant chain-stoppage mechanism.