Sorption experiments have been conducted at temperatures between 65 and 135degreesC using five phenolic antioxidants in polycarbonate at different antioxidant concentrations. A model based on the free volume was used to predict the mobility of the additives. In this model, the ratio of the specific volume of a jumping unit to the free volume available in the polymer determines the diffusion behavior of the additives. It was found that the mobility of the antioxidant was predicted accurately using literature and experimental data on the free volume in polycarbonate. Furthermore, the solubility of the antioxidants was predicted very well, based on thermodynamic considerations. (C) 2003 Wiley Periodicals, Inc.