Santosh C. Kumbharkar

Investigation of gas permeation properties of systematically modified polybenzimidazoles by N-substitution

Abstract Gas permeation behavior of a series of thermally stable N -substituted polybenzimidazoles by systematically varying bulk and flexibility of the substituent was investigated. Two different PBIs having variation in their acid moiety, viz., PBI-I (based on isophthalic acid) and PBI-BuI (based on 5- tert -butyl isophthalic acid) were selected for N -substitution by alkyl groups possessing different bulk and flexibility. These substituent groups were methyl, n -butyl, methylene trimethylsilane and 4- tert -butylbenzyl. Pure gas sorption and permeability using H 2 , N 2 , O 2 , CH 4 and CO 2 were investigated and correlated with physical properties of formed polymers. Estimation of dual-mode sorption parameters, coefficients of sorption, permeability and diffusion for different gases provided an insight towards effects of nature of a substituent group and parent PBI on governing gas sorption and permeation properties. By changing the substituent group, diffusivity coefficients was found to vary to a larger extent than the solubility coefficient. This significantly enhanced gas permeability for different gases by 1.2–129 times than that of parent PBIs. The permselectivity P O 2 / P N 2 was increased (up to 237%), while for other gas pairs, it was decreased to a different extent.