Gas transport properties of fluorinated poly(ether imide) films containing phthalimidine moiety in the main chain

Gas transport properties of five new fluorinated poly(ether imide) (PEI) films containing cardo phthalimidine moiety in the main chain were systematically investigated at three different temperatures (35, 45 and 55 °C) under an applied upstream pressure of 3.5 bar. The effect of presence of the cardo phthalimidine unit and structural variations of five aromatic dianhydrides in these poly(ether imide) (PEI) films towards the gas permeation of four gases (e.g., CO2, O2, N2 and CH4) and their permselectivity for pair of gases were investigated. The films were prepared by the thermal imidization of the poly(amic acid)s of the reaction products of a new fluorinated diamine, 3,3-bis-[4-{2′-trifluoromethyl 4′-(4″-aminophenyl)phenoxy}phenyl]-2-phenyl-2,3-dihydro-isoindole-1-one with five different dianhydrides namely, BPADA, 6-FDA, BTDA, ODPA and PMDA. All the PEI films exhibited significantly high permeability coefficients than those of common glassy polymers, e.g., cellulose acetate, polysulfone and polycarbonate as well as to other polymers based on cardo phenolphthalein or phthalimide or phthalimidine moiety. PEI-II and PEI-V showed exceptionally high permeability coefficient for all the gases (PCO2=53.85,39.57PCO2=53.85,39.57 Barrers, respectively) along with higher permselectivity towards CO2 relative to CH4 (53.32 and 50.09, repectively) in comparison to cardo phthalimidine based non-flourinated poly(arylene ether sulfones) reported previously. Moreover, high permeability coefficients for O2 (PO2=10.23,7.62PO2=10.23,7.62 Barrers, respectively) and comparable permselectivities towards O2 relative to N2 (4.4–6.35) made these series of PEI films highly interesting in comparison to the previously reported phthalimidine based poly(arylene ether sulfone)s or poly(arylene ether ketone)s. Temperature dependency of the permeation and diffusion processes enables to calculate the activation energies of the permeation and diffusion processes for these four different gases through these five PEI films. An attempt has been taken to draw a structure–property correlationship between the repeat unit structures or the functional groups present, and the gas transport properties of this series of PEI films.