Gas transport properties of 6FDA-durene/1,3-phenylenediamine (mPDA) copolyimides

The gas transport properties of He, H₂, O₂, N₂, and Co₂ for 6FDA-durene, 6FDA-mPDA, and their copolyimides have been investigated as a function of the composition, pressure, and temperature. The permeabilities, diffusion coefficients, and solubility coefficients follow the simple additional rules and Arrhenius relationships for 6FDA-durene/mPDA polyimides. The permeability decreases with an increase in pressure except He, and in the kinetic diameters of the penetrant molecules with the order of He, Co₂, O₂, and N₂. The diffusion coefficients of O₂, N₂, and CO₂ increase with increasing pressure and temperature. Interestingly, for these polyimides, the diffusion coefficient of O₂ is larger than that of CO₂. This may be caused by the strong quadrupole moment of the CO₂ molecules or the difficulty in estimating the accurate diameter of CO₂ molecules. The solubility coefficients decrease in the order of inherent condensability of the penetrant gases, namely CO₂, O₂, and N₂. In addition, WAXD results show that 6FDA-durene/mPDA polyimides are amorphous. The presence of a single glass transition temperature for these copolyimides indicates that these polyimides can be assumed to be random copolymers. They have excellent thermal stability exhibiting degradation temperature in a range of 493 to 548°C.