Poly( methyl methacrylate-ran-perfluoroalkyl ethyl methacrylate) copolymers having varying perfluoralkyl ethyl methacrylate ester (Zonyl-TM) contents were synthesized in supercritical CO2. 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.