Study of the relaxation properties of elastomers using a diffusion method

The high temperature relaxation transition in polyisoprene (SKI) and butyl rubber has been investigated, using a diffusion method. As the molecular weight of a polymer increases up to some critical value the diffusion coefficient of solid low molecular weight substances in homopolymers is rapidly reduced and, after attaining a critical MW value, remains constant. The very sparse crosslink network suppresses the high temperature transition, and reduces the diffusion coefficient. Mechanical treatment leads to a reversible reduction in the diffusion coefficient. Values of relaxation times for restoration of the polymer structure after mechanical treatment have been estimated from the diffusion data.