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

This manuscript describes the gas transport properties of five new fluorinated poly(ether imide) membranes containing indan moiety in the main chain. The membranes were prepared from the poly(amic acid)s of the reaction products of an unsymmetrical indan containing fluorinated diamine monomer, BPI with five different commercial dianhydrides namely, PMDA, BTDA, 6FDA, ODPA, and BPADA in DMF. Controlled thermal imidization was adopted to get dense polyimide membranes. Four gases, CO2, O2, N2 and CH4, were used in this investigation. The measurements were conducted at 35, 45, and 55 °C under an applied upstream pressure of 3.5 bar. All these polymeric membranes showed higher gas permeability with comparable permselectivity in comparison to many other indan containing polyimides reported earlier. Among these polyimides membranes, BPI-6FDA containing hexafluoroisopropylidine group showed the highest ideal CO2 permeability coefficient of 57.45 barrer with a permselectivity of 35.46 for CO2/CH4. The membrane BPI-BTDA showed the highest permselectivity of 38.86 for CO2/CH4 whereas BPI-ODPA showed the highest selectivity of 6.30 for O2/N2. The effect of temperature on the gas transport properties of these membranes was also studied. The activation energies for gas permeation and diffusion processes were calculated from the corresponding Arrhenius plots. An attempt has been made to draw a structure–property correlationship between the gas transport properties of these newly prepared membranes with their different chemical structures.