The gas permeability, diffusivity, and solubility of a series of polysulfones bearing basic aryl substituents were determined at 35 degrees C and pressures up to 20 atm. Gas permeability and diffusivity values of the aryl-substituted polysulfones were markedly lower than those of unmodified polysulfone. These effects were ascribed to decreased fractional free volume and increased restriction to sub-T-g torsional motion in the substituted polymers. Polysulfone bearing benzylic amine substituents exhibited higher CO2 solubility and CO2/CH4 solubility selectivity than polysulfone, presumably due to favorable interactions between acidic CO2 molecules and basic-CH2-NH(2)groups. CO2 diffusivity in polysulfone bearing benzylic amine substituents is lower than expected based on free volume considerations, suggesting that interactions between CO2 and benzylic amine moieties may be strong enough to impede CO2 mobility in the modified polymer. These results are consistent with infrared spectroscopy data which suggest that the benzylic amino groups undergo reversible reaction with CO2 to form carbamate moieties.