High temperature free radical polymerization. 2. Modeling continuous styrene polymerization

A comprehensive kinetic model for the thermal polymerization of styrene at temperature values between 250 and 350 degreesC, capable of calculating monomer kinetics, oligomer concentrations, and molecular weight and terminal double bond (TDB) distributions, is described. The model, based on the mechanism described in the first part of this work (Macromolecules 2003, 36, 0000), accounts for polymerization, thermal initiation, and degradation reactions, including backbiting, chain transfer to polymer, and addition to terminal unsaturation, all followed by beta-scission. All activation energies for the rate parameters were taken from independent literature sources, with the exception of backbiting for which the experimental data obtained in part 1 of this work have been used. The frequency factors for the backbiting, chain transfer to polymer, and addition fragmentation reactions were fitted using a combination of molecular weight, oligomer concentration, and terminal double bond distribution (TDB) data for three different temperature values. Using these parameter values, the model was found to adequately predict the oligomer concentrations, molecular weights, and TDB distributions over the entire range of experimental conditions examined in the first part of this work. The kinetic model indicates that this polymerization is characterized and controlled by aggressive backbiting, followed by beta-scission degradation.