Molecular weight distribution in thermal polymerization of styrene

The molecular weight distribution in thermal polymerization, for which the termination rate is comparable with the transfer rate, is analyzed by assuming that (1) the termination rate is independent of chain length; (2) the rate is translational diffusion‐controlled; and (3) the rate is influenced by the excluded volume. The theoretical distribution, based on the assumption that the rate is translational diffusion‐controlled, is the best fit to the experimental data at high temperature. The dependence of the rate on chain length is stronger at higher temperature (>80°C). The ratio of the termination rate to the transfer rate increases with increasing temperature.