DIFFUSION IN GLASSY-POLYMERS - RELAXATION AND ANTIPLASTICIZATION

The applications of free-volume concepts to describe diffusion in polymer-solvent systems is reviewed. It is shown how the Vrentas-Duda free-volume model for diffusion in polymer solutions above the glass transition temperature can be modified to describe diffusion of low molecular weight species in glassy polymers. The free-volume model for the diffusion of a trace amount of solvent in a glassy polymer is evaluated utilizing data for toluene-polystyrene. The inverse gas chromatography technique using a capillary column coated with a polymer film was employed to obtain diffusivity data for the toluene-polystyrene system over a temperature range traversing the glass transition temperature. Finally, it is discussed how free-volume concepts can be extended to describe antiplasticization behavior which occurs when molecular motions in glassy polymers are retarded by the addition of certain low molecular weight species.