THE EFFECT OF ARYL NITRATION ON GAS SORPTION AND PERMEATION IN POLYSULFONE

CO2, CH4, O-2, and N-2 permeability and solubility of unmodified and aryl-nitrated polysulfone were determined at 35 degrees C and pressures up to 20 atm. The degree of nitration was varied from O to 2 nitro groups per repeat unit. The permeability and diffusion coefficients for all gases decreased with increasing degree of nitro substitution. The decrease in gas diffusivity is attributed to a combination of decreased fractional free volume and decreased torsional mobility with increasing degree of substitution. The solubilities of N-2, O-2, and CH4 do not show a systematic dependence on degree of substitution. However, CO2 solubility apparently goes through a minimum as the degree of substitution is increased. CO2 solubility may be influenced by a competition between increases in polymer polarity (favoring higher solubility) and lower free volume (favoring lower solubility) that accompanies increases in the polar nitro substituent concentration. CO2/CH4 solubility selectivity increases monotonically as the degree of substitution increases. CO2/CH4 permselectivity and diffusivity selectivity increased with increasing degree of substitution. (C) 1995 John Wiley & Sons, Inc.