Gas and hydrocarbon (C 2 and C 3) transport properties of co-polyimides synthesized from 6FDA and 1,5-NDA (naphthalene)/Durene diamines

Abstract

The intrinsic gas permeabilities, diffusivities and solubilities of O 2, N 2, CH 4, CO 2, and those of the olefin and paraffins, C 2H 6, C 2H 4, C 3H 8 and C 3H 6 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, CO 2/CH 4 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 C 2H 6 and C 2H 4 plasticization was detected for these copolymers even at the testing pressures up to 1,621,200 Pa (16 atm). However, plasticization was observed for C 3H 8 and C 3H 6 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 C 2H 4/C 2H 6 and C 3H 6/C 3H 8 selectivities for some polymers is also made.