Diffusion‐controlled reactions in free radical polymerisation

Abstract

Abstract The evidence that the rates of radical – radical recombination reactions in solution are diffusion‐controlled is assessed and the consequences of diffusion‐controlled termination reactions in radical polymerisation examined. The cross‐termination rate coefficients for two different radicals should be the sum of the two mutual‐termination rate coefficients of these radicals. The frequently used geometric mean relationship is not relevant to diffusion‐controlled reactions. The dependence of the diffusion‐controlled k t on the size of the macroradicals and its effect on the rate equation for polymerisation is examined. The nature of the mean value, k̄ t, which is measured experimentally, is discussed. The role of diffusion‐control at high conversion is discussed. It is shown that simple diffusion‐control of the propagation reaction is incompatible with the observed diffusivities of small molecules in polymer gels.