A comprehensive kinetic model for the combined chemical and thermal polymerization of styrene up to high conversions

In the present study, a comprehensive mathematical model is developed for the free-radical polymerization of styrene to predict the polymerization rate and the molecular-weight distribution of the polymer. The kinetic model accounts for both chemical and thermal radical generation and, thus, can be employed over an extended range of polymerization temperatures (e.g., 60-200degreesC). The thermal initiation mechanism includes the reversible Diels-Alder dimerization of styrene, radical formation via the reaction of the Diels-Alder adduct with monomer, the formation of dead trimers and the initiation and the initiation of new polymer chains. Moreover, a comprehensive free-volume model is employed to describe the variation of termination and propagation rate constants as well as of the initiator efficiency with respect to the monomer conversion. The cumulative molecular-weight distribution of the polystyrene is calculated by the weighted sum of all the 'instantaneous' weight chain-length distributions formed during the batch run. The capabilities of the present model are demonstrated by a direct comparison of model predictions with experimental data on monomer conversion, number- and weight-average molecular weights, and molecular-weight distribution. It should be noted that previously published kinetic models cannot describe the combined thermal and chemical free-radical polymerization of styrene in terms of a unified, fundamental, kinetic model, which further underlines the significance of this study.