AbstractAnalysis of results of experiments on dielectric relaxation of polyvinyl chloride plasticized with tricresyl phosphate and with dioctyl phthalate gives values for heats and entropies of activation for dielectric relaxation rather lower than have been published in the literature for lower frequency ranges. The discrepancy may be due to a variation of heat of activation with temperature. A theoretical relation has been derived for the variation of heat and entropy of activation of dielectric relaxation with plasticizer content. The temperature dependence of the secondary high frequency loss factor maximum in unplasticized PVC has been ascertained, and some aspects of the relation between electrical and mechanical relaxation times and the second‐order transition point have been discusse