Effect of Basic Substituents on Gas Sorption and Permeation in Polysulfone

The gas permeability, diffusivity, and solubility of a series of polysulfones bearing basic aryl substituents were determined at 35 °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 CO 2 solubility and CO 2 /CH 4 solubility selectivity than polysulfone, presumably due to favorable interactions between acidic CO 2 molecules and basic −CH 2 -NH 2 groups. CO 2 diffusivity in polysulfone bearing benzylic amine substituents is lower than expected based on free volume considerations, suggesting that interactions between CO 2 and benzylic amine moieties may be strong enough to impede CO 2 mobility in the modified polymer. These results are consistent with infrared spectroscopy data which suggest that the benzylic amino groups undergo reversible reaction with CO 2 to form carbamate moieties.