Modeling of termination in intermediate and high conversion free radical polymerizations

A simple means of modeling termination in free radical polymerizations of a large number of monomers over a wide variety of intermediate and high conversion conditions is presented. It is shown that monomers can be divided into two classes according to the qualitative variation of their termination rate coefficient (kt) with conversion (U). It is then suggested that it is profitable to represent kt data as kt/[kp·(1 − U)]. Doing this reveals that over a wide range of temperatures and of intermediate and high conversions, seemingly complex variations of kt with U can be described by a single parameter (CRD), the value of which varies from monomer to monomer. Proceeding from the idea that the process of reaction-diffusion is the rate determining mechanism of termination, two easily implementable models for a priori prediction of CRD are developed in parallel from already existing ideas. One of these models is shown to predict with remarkable accuracy a large variety of experimental CRD data. Slight modification of these predictions makes this model even more accurate, and therefore gives it great potential for modeling purposes.