Contributing to a better comprehension of: the styrene bulk free-radical polymerization with n-pentane added as a blowing agent for producing expandable polystyrene

The kinetic study of free radical polymerization of styrene in the presence of n-pentane is a challenging and relevant topic because of its commercial and scientific value. Although this reaction has been carried out for decades, its kinetics are not fully understood. Thus, this polymerization is a current research topic mainly focused on the diffusive effects and ways to make more economical and efficient processes. This work presents a study focused on analyzing the kinetic effect of n-pentane addition during the bulk free-radical polymerization of styrene to contribute to the comprehension of phenomena which take place during this reaction. To reach this goal, we extended and implemented a model previously developed by one of the authors to perform the simulation and prediction of experimental data reported in the literature at different reaction conditions and multiple n-pentane amounts. Results obtained with the model allow us to explain the polymerization evolution in terms of the diffusive effects and the explicit theoretical description of the repetitive units that a terminal segment from a long radical involved in the termination stage can move (U_segm). That lets us identify the effects produced by the presence of n-pentane in the theoretical transition region from chemical to diffusive control in the termination reaction. This region is relevant due to its relationship with the increasing polymerization rate and the onset of the auto-acceleration effect. The comparison of the theoretical evolution of the weight-average molecular weight (M_w) against experimental data indicates that to enhance their correlation is necessary to consider not only the solvation effect but also the transfer effect produced by the presence of n-pentane during the polymerization.