A mathematical model is proposed for predicting small molecule solvent diffusion coefficients in amorphous glassy polymers

based on free volume theory that is suitable for rubbery polymers

and with the consideration of the plasticization effect induced by the penetrant. Because this model uses the identical conceptual framework in which free volume theory is derived for solvent diffusion in rubbery polymers

parameters used in free volume theory remain valid for this work. Only one parameter is introduced to describe the plasticization effect

and it can be easily estimated by thermodynamic theory about the glass transition temperature depression. Therefore

no adjustable parameters appear in this expression

resulting in its usefulness in prediction. Comparison of the diffusion coefficients calculated by this new model with the present experimental data

including benzene

toluene

ethylbenzene in polystyrene (PS) and poly(methyl methacrylate) (PMMA) are performed

calculation results in this study are in good agreement with experimental data

for the correct estimation of the hole-free volume change above and below the glass transition.