Gas Transport Properties of 6FDA-Durene/1,3-Phenylenediamine (mPDA) Copolyimides

摘要

The gas transport properties of He, H_2, O_2, N_2, and CO_2 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 Arrihenuis 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, CO_2, O_2, and N_2. The diffusion coefficients of O_2, N_2 and CO_2 increase with increasing pressure and temperature. Interestingly, for these polyimides, the diffusion coefficient of O_2 is larger than that of CO_2. This may be caused by the strong quadrupole moment of the CO_2 molecules or the difficulty in estimating the accurate diameter of CO_2 molecules. The solubility coefficients decrease in the order of inherent condens-ability of the penetrant gases, namely CO_2, O_2 and N_2. 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 548deg C.