Experimental and Theoretical Study of the Bulk Polymerization of Styrene Using the Symmetrical Cyclic Trifunctional Initiatior Diethyl Ketone Triperoxide (DEKTP)

This work experimentally and theoretically investigates the use of the symmetrical cyclic trifunctional initiator diethyl ketone triperoxide (DEKTP) in the bulk polymerization of styrene (St). The experimental work involved a series of isothermal batch polymerizations at different temperatures,120 and 130°C, with different initiator concentrations: 0.005, 0.01 and 0.02 mol/L. Conversion and average molecular weights were measured from samples taken along the polymerization reaction. Experimental results show that DEKTP initiation produces an increase in polymerization rates and average molecular weights, due to sequential decomposition of the initiator molecules. The theoretical work consisted on the development of a mathematical model that predicts the evolution of the chemical species and the molecular weight distributions during the polymerization. The model is based on a kinetic scheme that considers chemical and thermal initiation, propagation, transfer to the monomer, termination by combination and re-initiation reactions. Random scission and uniformly distributed peroxide 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 peroxide groups. The mathematical model was adjusted and validated using the experimental data. Theoretical estimates are in excellent agreement with measurements obtained. For the sought experimental conditions, simulations indicate the presence of polymeric species with more than 20 undecomposed peroxide groups at the end of the polymerization reaction, and an average of 3 undecomposed peroxide groups per chain.