Abstract
AbstractThe theory of Kuhn and Kuhn for the diffusion of polymer chain ends has been applied to the termination mechanism for free radical polymerizations, proposed by Benson and North. By using the dimensions for a Gaussian chain, an expression for this diffusion‐controlled termination rate constant in terms of solvent viscosity, polymer chain flexibility, and chain length has been derived. The theory predicts that the termination rate constant is inversely proportional to solvent viscosity for flexible polymer chains and independent of solvent viscosity for very stiff polymer chains. Several previously reported effects of solvent viscosity on the termination rate constant may be explained with the present theory. The effect of polymer chain length on the termination rate constant depends upon the range of chain lengths considered and upon the relative chain stiffness. The necessity of taking into account the frequency distribution of radicals which exists during polymerization is discussed. Calculated values of the termination rate constant have been carried out with the use of values for the various parameters which are believed to be typical of vinyl polymers in solution. These calculated values are in general agreement with those which are usually obtained experimentally.
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