Gas sorption and permeation in PIM-1

Abstract

Gas transport properties of PIM-1, i.e., the first “polymer with intrinsic microporosity,” at 25°C and different pressures were systematically studied. Permeability coefficients of 10 gases including He, H2, N2, O2, CH4, CO2, C2H4, C2H6, C3H6 and C3H8 were conducted at 25°C for five different upstream pressures (from 1 to 10atm). The C2 and C3 hydrocarbons exhibited serious plasticization responses while the permeability coefficients of He, H2, O2, N2, CH4 and CO2 decreased with the trans-membrane pressure as expected from the dual-mobility model. Sorption isotherms of all 10 gases were also determined using a dual-volume sorption cell at 25°C up to a maximum pressure of 27atm. The sorption isotherms followed the dual-mode sorption model. The logarithm of the solubility coefficients increased linearly with the critical temperature of the gas and the slope of this plot (0.018) was found to be comparable with values reported for other glassy polymers. Diffusion coefficients were calculated from the permeability and solubility data; the values for He, H2, O2, N2, CH4 and CO2, increased with pressure as predicted by the dual-mobility model while those of the C2 and C3 hydrocarbon gases increased more strongly because of plasticization. Parameters from the dual mobility model, DD and DH, were significantly higher and their ratio, DH/DD was significantly smaller than those of previously reported polymers.