Poly( methyl methacrylate-ran-perfluoroalkyl ethyl methacrylate) copolymers having varying perfluoralkyl ethyl methacrylate ester (Zonyl-TM) contents were synthesized in supercritical CO(2). Complete amorphous structures of the copolymers were verified by XRD. Young's modulus (Y(mod)) of the copolymers was decreased linearly from 1.57 to 1.08 GPa and T(g) values from 102 to 77 C with the increase of Zonyl-TM content. A linear relationship between the Y(mod) and the T, values of the copolymer was also found. The increase of the large branched pendant groups resulted in the increase of the free volume and a corresponding decrease in Ymod and T(g) of the copolymers. A good fit was found when the Schneider equation was used. Negative deviation from the Gordon-Taylor equation was observed when Zonyl-TM content was lower than 14% due to rapid increase in free volume and then a positive deviation was found due to the dipole-dipole interactions between the methyl ester and fluoroalkyl ester groups. (C) 2011 Elsevier B.V. All rights reserved.