Mathematical Model for the Bulk Polymerization of Styrene in the Presence of Polybutadiene Using a Trifunctional Initiator

A detailed mathematical model for the bulk polymerization of styrene in the presence of polybutadiene using the trifunctional initiator diethyl ketone triperoxide (DEKTP) was developed with the aim of simulating a bulk high-impact polystyrene (HIPS) process. The model predicts the evolution of the chemical species and the detailed molecular structures in the course of the polymerization and is based on a kinetic mechanism that considers chemical and thermal initiation, propagation, transfer to the monomer, transfer to the rubber, termination by combination and re-initiation reactions, together with volume contraction and gel effect. Simulation predicts the concentration of di- and monoradicals as well as the concentration of polymeric species for free polystyrene, residual polybutadiene and graft copolymer, characterized by both chain length and number of undecomposed peroxide groups. The continous model allows obtaning the complete molecular weight distributions and detailed composition of the resulting polymeric species in very short simulation times. The model was adjusted and validated using experimental data corresponding to a batch HIPS process using DEKTP at different temperatures (120-130 ºC) and different initiator concentrations (0.79 – 3.12 mmol/L). Conversion, average molecular weights of free polystyrene, product composition and grafting efficiency were measured from samples taken along the reaction. Theoretical estimates of the proposed mathematical model are in very good agreement with the measurements.