Gas separation properties of aromatic polyamides with sulfone groups

Abstract

The gas transport properties of three aromatic polyisophthalamides based on isophthaloyl chlorides and 4,4′-diaminodiphenylsulfone are reported at 35°C. The effects of bulky t-butyl and phthalimide substituents, at the 5 position of the isophthaloyl chloride moiety, on CO2, CH4, O2, N2, H2 and He permeability, solubility and diffusivity were determined and correlated with chain packing and thermal properties of the polymers. Gas permeability was higher in substituted polyisophthalamides than in the unsubstituted analogue. Polymers containing the pendent t-butyl substituent have substantially higher permeability than polymers bearing the phthalimide substituent, despite the fact that the phthalimide substituent appears to be more bulky than the t-butyl group, based on van der Waals volume estimations. The strong polarity of the phthalimide moiety may act to increase chain-chain cohesive forces, which would tend to enhance chain packing, thereby reducing the packing-disrupting ability of the bulky phthalimide group. The permeability increase of the substituted polymers was accompanied by a permselectivity decrease.