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The intrinsic gas permeabilities, diffusivities and solubilities of O 2 , N 2 , CH 4 , CO 2 , and those of the olefin and paraffins, C 2 H 6 , C 2 H 4 , C 3 H 8 and C 3 H 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 2 H 6 and C 2 H 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 3 H 8 and C 3 H 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 2 H 4 /C 2 H 6 and C 3 H 6 /C 3 H 8 selectivities for some polymers is also made.

Mixed matrix membrane is a highly potential material that may possibly overcome the challenges faced by the membrane technology today. We explored the gas separation performance of a modified Matrimid/C60 mixed matrix membranes. The membranes were prepared by physically blending a series of benzylamine-modified fullerene, C60 with pure Matrimid 5218. The bulk Matrimid and the dispersed benzylamine-modified fullerene molecules show strong interfacial interactions as reflected by a significant increase in the Tg of the film with C60 loading. Gas permeabilities of He, O2, N2, CH4, and CO2 show a monotonous decrease with increasing benzylamine-modified C60 content. The percentage of permeation reduction at 10 wt.% benzylamine-modified C60 loading is 32% for He (kinetic diameter of 2.6 A), while 41.7 and 41.5%, respectively, for the O2 (3.46 A) and N2 (3.64 A) gas pair, 45.2 and 47.0%, respectively, for CH4 (3.8 A) and CO2 (3.3 A) gas pair. The decrease of the gas permeability with increasing C60 compositions is found to be mainly due to the decrease in the gas diffusivity. The presence of the benzylamine-modified C60 seems to serve as impenetrable volumes and rigidifying elements within the polymer matrix. Therefore, the diffusivity of larger penetrants is reduced to a greater extent than the smaller penetrants and results in the increase of He/N2 selectivity. This is also supported by the sorption data, which reveals that the Langmuir sorption capacity decreases with increasing C60 loading. The increase in the glass transition temperature and the measured density indicate that the presence of the chemically modified C60 molecules have rigidified the polymer and pulled the matrix together.

The transport of olefin and paraffin namely ethane, ethylene, propane and propylene in aromatic poly(1,5-naphthalene-2,2′-bis(3,4-phthalic) hexafluoropropane) diimide (6FDA-1,5-NDA) dense membranes was investigated. The gas permeability coefficients were measured at pressures from 2.5 to 16 atm for the C 2 hydrocarbon gases and pressures up to 8.4 atm for C 3 systems at 35 °C. This membrane exhibits permeabilities of 0.15, 0.87, 0.023 and 0.24 Barrer with respect to pure ethane, ethylene, propane and propylene, and shows an ideal selectivity of 5.8 for the separation of ethylene/ethane, 10 for propylene/propane, 7.6 for nitrogen/ethane and 50 for nitrogen/propane. The olefins showed a preferred permeability to paraffins and discussion were drawn to the permeability, diffusivity and solubility coefficients. The activation energies of permeation, diffusion and solution were also reported and the effect of temperature on the permeation properties was discussed for the pure gas permeability data obtained from 30 to 50 °C. The plasticisation effect was also found for propane and propylene, respectively, although it was neither detected in the saturated nor unsaturated C 2 hydrocarbons at pressures up to 16 atm.

The intrinsic gas transport properties of permeation, diffusion and sorption for He, O 2 , N 2 , CH 4 and CO 2 in aromatic polyimide, poly(1,5-naphthalene-2,2′-bis(3,4-phthalic) hexafluoropropane) diimide (6FDA-1,5-NDA) dense membranes were investigated. The permeation of pure gases of He, O 2 , N 2 , CH 4 and CO 2 was measured with a temperature-controlled permeation cell while the sorption isotherm was obtained from the Cahn 2000 microbalance sorption cell. The 6FDA-1,5-NDA membrane has a selectivity of 49 for CO 2 /CH 4 with a permeability of 22.6 Barrers for CO 2 under 10 atm at 35 °C. The Henry’s diffusivity holds a dominating effect over the Langmuir diffusivity and decreases in the order of O 2 >CO 2 >N 2 >CH 4 , in fair agreement with the apparent diffusivity. The activation energies of permeation and diffusion increase with increasing gas kinetic diameters in the order of CO 2 , O 2 , N 2 and CH 4 . The solubility of gases tested adopts a parallel trend with their critical temperatures. Upon pressure acceleration, the gas diffusivity increases while the solubility decreases. The overall gas permeability of 6FDA-1,5-NDA decreases with increasing pressure, which can be explained by using the dual-mode sorption model and the partial immobilisation model. More than 50% of the entire total gas sorbed is distributed in the Langmuir environment when pressure is less than 25 atm. The fractional mobility of Langmuir species decreases while the fractional mobility of the Henry species increases when the feed pressure increases. CO 2 exhibits the most significant pressure-dependent properties due to its the strongest interaction and highest condensability.