Prediction of Solvent Diffusivities in Amorphous Polymers by Free-Volume Theory: Group Contribution and PALS Methods

A group contribution-based model was proposed to predict solvent diffusion coefficients in amorphous polymers with the free-volume conceptual framework. Based on the van der Waals Volume of polymer structural units, this model provides a novel way to estimate the hole free volume of polymer in its rubbery state, which is the effective space for solvent jump. All the parameters with respect to polymer can be determined by group contribution method using the knowledge of polymer structure. and no adjustable parameters are required. Calculated solvent diffusion coefficients in polymers were in good agreement with published experimental results. A linear dependence was found between logarithm of infinite dilution diffusion coefficient of various organic solvents and hole free Volume in four common polymers. In addition, the hole size distribution from positron annihilation lifetime spectroscopy (PALS) measurements was investigated to reaffirm the reliability of this model, on the basis that the ratio of polymer hole free volume to total free volume from microscopic viewpoint should be equivalent to that from macroscopic viewpoint.