Free Radical Copolymerization Kinetics of Styrene/Divinylbenzene

Abstract

<p>An effective model for the bulk, solution and suspension copolymerization of styrene/divinylbenzene (OVB) has been developed. Its effectiveness is understood as a compromise between sound theoretical basis and simple mathematical structure, which makes possible the solution of its governing equations using conventional computational tools.</p> <p>To build the model a comprehensive analysis of the elementary reactions and restrictions caused by the physical environment imposed by the growing polymer was made. The main issues considered in the model are: diffusion-controlled initiation, propagation and bimolecular termination reactions; different reactivities of double bonds; effect of solvent, chain transfer agent, inhibitor, type of crosslinker (m-DVB, p-DVB or mixtures of both), type of initiator; as well as crosslinking and primary-secondary cyclization reactions.</p> <p>In building the model, it was necessary to review and improve the conventional theory of diffusion controlled free radical polymerization kinetics. Important contributions in this area came out as a result. Among those contributions, the most important are: the demonstration that using a "parallel" approach for modelling effective kinetic constants which are "diffusion-controlled" (widely used in this field) is incorrect, the proposal of an effective way to calculate molecular weight averages, and the proposal of a model for calculation of non-equilibrium free volume.</p> <p>By performing a detailed compilation and analysis of experimental information available in the literature, all our objectives could be satisfactorily accomplished without having to perform additional experiments. Most of the experimental data and model predictions are in excellent agreement for pre and post-gelation periods. However, it is recognised that the real behavior of the polymerizing system is so complex (even the experimental techniques for characterization of network polymers are still in the development stage), that the model developed herein must be considered as a first realistic approximation to the real situation. Some guidelines for the improvement of this model (mostly associated to secondary cyclization) and preliminary qualitative calculations associated to these modifications have been given.</p>