An investigation of the kinetics of copolymerization of p-methylstyreneacrylonitrile to high conversion: Modelling diffusion-controlled termination and propagation by free-volume theory

An experimental investigation of the kinetics of the bulk free-radical copolymerization of p-methylstyrene (PMS) and acrylonitrile (AN) initiated with azobisisobutyronitrile was conducted at temperatures of 40, 60 and 80°C. Two levels of initiator concentration and three initial monomer compositions were studied. Conversions were measured gravimetrically and by gas chromatography. Weight average molecular weights were measured by low-angle laser light scattering photometry and size exclusion chromatography, and number average weights by size exclusion chromatography. A kinetic model incorporating free-volume theory seems to account reasonably for diffusion-controlled termination and propagation. The model also accounts for segmental-diffusion control of termination rate at low conversion and termination by reaction diffusion at high conversion. Model predictions are in reasonable agreement with experimental data on copolymerization of these monomers. This model should find use in the design, simulation, optimization and control of polymer reactor systems for the production of PMS/AN copolymers.