(163f) Mathematical Model for the Bulk Polymerization of Styrene Using Symmetrical Cyclic Multifunctional Initiators

A novel mathematical model for bulk polymerization of styrene using cyclic multifunctional initiators was developed in order to predict the evolution of the chemical species and the detailed molecular structure during the polymerization. The model is based on a kinetic scheme that considers chemical initiation, by both sequential and total initiator decomposition, thermal initiation, propagation, transfer to the monomer, termination by combination and re-initiation reactions. Random scission and uniformly distributed labile groups in the polymeric chains were assumed in order to model the re-initiation reactions. Simulation results predict the concentration of di- and monoradicals as well as polymeric chains, characterized by the number of undecomposed labile groups. The mathematical model was adjusted and validated using experimental data obtained from bulk polymerizations of styrene using the cyclic trifunctional initiator diethyl ketone triperoxide (DEKTP). Theoretical estimates are in excellent agreement with measurements.  In the experimental work, several isothermal batch polymerizations were carried out at different temperatures and different initiator concentrations. Conversion and average molecular weights were measured from samples taken along the reaction. For reaction temperatures of 120-130 ºC, initiator decomposition was found to be mostly by sequential rupture, allowing high polymerization rates and high molecular weights simultaneously. For reactions temperatures above 130 ºC, a total rupture mechanism is dominating, resulting in lower molecular weights. Experimental and theoretical results show the existence of optima for temperature and initiator concentration in order to obtain high productivity and increased product quality. The model may be extended to simulate other free radical polymerization systems using different cyclic multifunctional initiators