Diffusion‐controlled vinyl polymerization. II. Limitations on the gel effect

Abstract It is frequently observed that the gel effect in vinyl polymerizations decreases in intensity at about the 50‐70% conversion level. This is apparent in both rate and molecular weight data. It is postulated that there should be a limitation on the decrease in the termination rate constant to explain this effect. As an extension of the general theory of chain length dependent termination behavior, a general treatment of the gel effect with a limiting value of the termination rate constant is presented. A specific model is proposed for this limited rate constant which is based on the simple consideration that as translational movement of macroradicals becomes increasingly difficult the contributions made by segmental motion derived solely from the propagation reaction will be the prevailing mechanism. The termination reaction changes from chain length dependent to chain length independent during this transition period.