Gas and hydrocarbon (C2 and C3) transport properties of co-polyimides synthesized from 6FDA and 1,5-NDA (naphthalene)/Durene diamines

The intrinsic gas permeabilities, diffusivities and solubilities of O2, N2, CH4, CO2, and those of the olefin and paraffins, C2H6, C2H4, C3H8 and C3H6 in aromatic co-poly(1,5-naphthalene/1,4-Durene-2,2′-bis(3,4-dicarboxyl phenyl) hexafluoropropane diimide) (6FDA–1,5-NDA/Durene copolyimides) with ratios varying at 75/25, 50/50 and 25/75 were reported for the first time. The gas transport properties of these materials for binary gas mixtures, CO2/CH4 were also investigated. Experimental results show that the gas permeability of copolymers follows the additional rule of semi-logarithmic equation and selectivity increases with increasing poly(1,5-naphthalene-2,2′-bis(3,4-phthalic) hexafluoropropane) diimide (6FDA–1,5-NDA) content mainly due to an increase in the diffusivity selectivity. Copolymers with higher 6FDA–NDA compositions show a better packing density, which most probably due to the enhanced interchain interactions resulting from the charge transfer complexes. No C2H6 and C2H4 plasticization was detected for these copolymers even at the testing pressures up to 1,621,200 Pa (16 atm). However, plasticization was observed for C3H8 and C3H6 because of their high condensability and strong polymer–penetrant interactions. The plasticization pressure is higher with an increase in 6FDA–NDA content in these copolymers. A comparison of C2H4/C2H6 and C3H6/C3H8 selectivities for some polymers is also made.