A Comprehensive Kinetic Model for the Combined Chemical and Thermal Polymerization of Styrene up to High Conversions

Abstract

AbstractIn 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., 60–200 °C). 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 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.Predicted and experimental weight‐average molecular weights with respect to monomer conversion (experimental conditions same as in Figure 1).magnified imagePredicted and experimental weight‐average molecular weights with respect to monomer conversion (experimental conditions same as in Figure 1).