The physical and gas permeation properties of 6FDA-durene/2,6-diaminotoluene copolyimides

The physical and gas transport properties of homo-polyimides, 6FDA-durene and 6FDA-2, 6-diaminotoluene (2,6-DAT), and their copolyimides, 6FDA-durene/2,6-DAT with different diamine ratios, were characterized. The glass transition temperatures of the copolyimides obtained from DSC experiments were about 6-10°C lower than that calculated from the Fox equation. The experimental results for the gas permeability, diffusivity and solubility of this series of polyimides fitted well with that predicted from the logarithm of property versus volume fraction. The gas permeability of 6FDA-durene/2,6-DAT decreased with increasing 6FDA-2,6-DAT content. However, the selectivity of gases pairs, such as CO₂/N₂, O₂/N₂ and H₂/N₂, increased with the addition of 6FDA-2,6-DAT. The permeability coefficients of H₂, He, O₂, N₂ and CO₂ decreased with the kinetic molecular diameters of the gas molecules, with an exception of helium. The diffusion coefficients for the gases of O₂, N₂ and CO₂ were found to decrease with the effective diameters of the penetrant molecules. The solubility coefficients of the gases increased with the condensability of the gas molecules. By decoupling the permselectivity of gas pairs of CO₂/N₂, O₂/N₂, it was found that the permselectivity of CO₂/N₂ was mainly controlled by the solubility selectivity, while in the gas pair of O₂/N₂, the permselectivity was dominated by the diffusivity selectivity.