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.