Modeling of diffusion‐controlled free‐radical polymerization reactions

Abstract

AbstractThe present paper introduces a new fundamental approach to the modeling of diffusion‐controlled free‐radical polymerization reactions. Our analysis follows the original work of Chiu, Carratt, and Soong (CCS), according to which the termination and propagation rate constants are expressed in terms of both a purely reaction‐limited term and a diffusion‐limited one. The contribution of the latter term to the apparent rate constants is described in terms of the polymer and monomer effective diffusion coefficients and an effective reaction radius. It is shown that all parameters appearing in the original CCS model can be calculated from first principles using available data on the physical and transport properties of a particular monomer–polymer binary system. The generalized free volume theory of Vrentas and Duda and the theory of excess chain end mobility are invoked for the calculation of the effective diffusion coefficients and the reaction radius, respectively. The approach followed in this study is general and needs only the specification of one unknown parameter with a clear physical meaning. All other parameters can be readily calculated from available data. The ability of the new model to predict molecular weight developments and monomer conversion in diffusion‐controlled reactions is demonstrated by application of the proposed model equations to the bulk polymerization of MMA.