Self-Diffusion Coefficients and Tack of Some Rubbery Polymers

Abstract

Abstract Self-diffusion coefficients for natural rubber, styrene butadiene rubber, ethylene propylene rubber and butyl rubber, are reported. Rates were determined by application of a layer of radioactively labeled polymer to the top of an unlabeled polymer base film and following the decay of radioactivity at the surface of the system, which decreased as a result of self-absorption. Macroscopically, diffusion is very slow, in fact difficult to measure, but on a microscopic scale it is rapid enough to cause considerable intermingling of polymer chains across an interface within a few seconds after two layers of polymeric material are brought into close contact. However, there were no major differences of self-diffusion coefficients between several types of polymers of comparable molecular weights. Therefore, the magnitudes of the coefficients suggest that diffusion may well be an important step for development of tacky adhesion, but the results also suggest that variations in observed tackiness among polymers cannot be simply ascribed to variations in diffusion rates.