Diffusion of Acetone into Polyvinyl Acetate above and below the Second-Order Transition

The sorption kinetics for the system polyvinyl acetate-acetone have been investigated both above and below 30°C, the second-order transition temperature for the pure polymer. At 30, 40, and 50°C, the diffusion obeys Fick's law with a concentration-dependent diffusion coefficient. With increasing acetone concentration the value of the diffusion coefficient increases strongly, and the energy of activation for diffusion decreases. At each temperature below 30°C, diffusion is Fickian only for sorption and desorption experiments where the solvent concentration is above a certain critical value. It was found, by comparison with the results of volume-temperature measurements on the system polyvinyl acetate-acetonyl acetone, that the temperature corresponding to a given critical concentration is the second-order transition temperature for this polymer-solvent mixture. Evidently, the changes which occur at the second-order transition have a pronounced influence on the diffusion process.