Modeling termination kinetics in free-radical polymerization using a reduced number of parameters

An approach for modeling chain-length dependent termination rate coefficients is presented. The method is based on the assumption that free-radical chain length may be considered as a continuous variable. As compared to discrete numerical methods, in continuous modeling the number of independent dimensionless parameters can be significantly reduced. As a consequence, for a wide variety of monomers the conversion dependence of kt can be predicted without extensive numerical calculations. The method may also be used to determine polymerization conditions under which simpler models of kt (which neglect effects arising from the dependence of kt on chain length) may be applied. Calculations for methyl methacrylate, styrene, and butyl acrylate bulk polymerizations up to high degrees of monomer conversion show that the impact of chain length on termination varies with conversion and strongly depends on the type of monomer.