The equilibrium sorption and swelling behavior of four different polymers-poly(methyl methacrylate), poly(tetrafluoroethylene), poly(vinylidene fluoride), and the random copolymer tetrafluoroethylene-perfluoromethylvinylether-in supercritical CO2- are studied at different temperatures (from 40 to 80 degrees C) and pressures (up to 200 bar). Swelling is measured by visualization, and sorption through a gravimetric technique. From these data, the behavior of amorphous and semicrystalline polymers can be compared, particularly in terms of partial molar volume of CO2 in the polymer matrix. Both poly(methyl methacrylate) and the copolymer of tetrafluoroethylene exhibit a behavior typical of rubbery systems. On the contrary, polymers with a considerable degree of crystallinity, such as poly(tetrafluoroethylene) and poly (vinylidene fluoride), show larger values of partial molar volume. These can be related to the limited mobility of the polymer chains in a semicrystalline matrix, which causes the structure to "freeze" during the sorption process into a nonequilibrium state that can differ significantly from the actual thermodynamic equilibrium. (c) 2006 Wiley Periodicals, Inc.