Effect of pressure on the propagation and termination rate constants of radical polymerization

The effect of high pressure on the propagating and terminating steps of free‐radical polymerization was summarized from our experimental data which were already described on the six polymerization systems: styrene, methyl methacrylate, butyl methacrylate, butyl acrylate, vinyl acetate, and octyl methacrylate. Using these data, the functional dependence of the rate constants for individual steps on pressure was investigated with a view to obtaining reliable values under high pressure. In practice, a linear function is the best description of the pressure dependence of the logarithmic propagation rate constant regardless of the polymerization type. It can be concluded, therefore, that the activation volume can be used as a pressure‐independent parameter for the propagating step in our pressure range (1–1000 bar). The empirical relation to estimate the pressure dependence of the propagating step for other polymerization systems was obtained from the correlation for the activation volumes and the volume contractions of polymerization. The effect of pressure on the termination step is also discussed. A quadratic polynomial is generally the best representation of the pressure dependence of the logarithmic termination rate constant.