Molecular interaction, gas transport properties and plasticization behavior of cPIM-1/Torlon blend membranes

Polymers of intrinsic microporosity, specifically PIM-1, have emerged as promising materials for gas separation due their high gas permeability. However, its insolubility in common polar aprotic solvents like N-Methyl-2-pyrrolidone (NMP) limits its full potential and possible industrial applications. In this study, the solubility of PIM-1 in such solvents has been modified by carboxylation via hydrolysis reaction in a short period of 1 h. The success of carboxylation was verified by nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared spectroscopy (FTIR) and water contact angles. The carboxylated PIM-1 (cPIM-1) was subsequently blended with Torlon to enhance the intrinsic permeability of Torlon rich membranes and the intrinsic selectivity of cPIM-1 rich membranes. The additions of 5, 10 and 30 wt% cPIM-1 into Torlon increase its CO2 permeability by 26%, 128% and 791%, respectively, from the original value of 0.541–0.682, 1.233 and 4.822 (1 Barrer=1 × 10−10 cm3(STP) cm/cm2 s cmHg=3.348 × 10−19 kmol m/m2 s Pa) with minor sacrifices in CO2/CH4 selectivity. These permeability improvements are attributed to the formation of hydrogen bonding and charge transfer complexes (CTC) between cPIM-1 and Torlon, which promotes better interactions in the blends. In addition, all the cPIM-1/Torlon membranes exhibit a great plasticization resistance up to 30 atm. This is ascribed to the incorporation of the rigid Torlon that may lead to restricting chain mobility in CO2 environments. The overall separation performance has been driven closer to the Robeson upper bound for O2/N2, CO2/CH4, CO2/N2 and H2/N2 separations. Therefore, the newly developed membranes may have great potential for energy development and industrial applications.