Solvent diffusion in amorphous glassy polymers

In this article, a mathematical model is proposed for predicting solvent se lf-diffusion coefficients in amorphous glassy polymers based on free volume theory. The basis of this new model involves consideration of the plastici zation effects induced by small molecular solvents to correctly estimate th e hole-free volume variation above and below the glass-transition temperatu re. Solvent mutual-diffusion coefficients are calculated using free volume parameters determined as in the original theory. Only one parameter, which can be predicted by thermodynamic theory, is introduced to express the plas ticization effect. Thus, this model permits the prediction of diffusion coe fficients without adjustable parameters. Comparison of the values calculate d by this new model with the present experimental data, including benzene, toluene, ethyl benzene, methyl acetate, and methyl ethyl ketone (MEK) in po lystyrene (PS) and poly(methyl methacrylate) (PMMA), has been performed, an d the results show good agreement between the predicted and measured values . (C) 2000 John Wiley & Sons, Inc.