Enhanced Gas Separation Performance of Thermally Rearranged Membranes with 2-Propyl-1 H -imidazole-4,5-dicarbohydrazide

Thermally rearranged (TR) membranes have recently demonstrated superior gas permeability and moderate ideal selectivity for gas separation applications. Herein, 2-propyl-1 H -imidazole-4,5-dicarbohydrazide (PIDH) was utilized as a modifier via a blending method to further improve the gas separation performance of TR membranes. Specifically, PIDH was blended into poly(amic acid) (PAA) solutions prepared from 2,2′-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP) and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA). These solutions were stepwise thermally treated to form polyimide (PI) membranes and corresponding TR membranes. PIDH effectively regulated the stacking behavior and intermolecular interactions of PI molecular chains. With the increase of its mass content from 0 to 0.5%, the glass transition temperature ( T g ) of the PI membranes was significantly elevated from 314 to 363 °C. After thermal rearrangement, all modified TR membranes exhibited notably enhanced gas permeability compared with the pristine TR membrane. Specifically, the TR membrane with 2.0% PIDH loading (TR-2.0%) showed excellent permeability coefficients: 112 Barrer for N 2, 2287 Barrer for H 2, 435 Barrer for O 2, and 2668 Barrer for CO 2 . In contrast, the TR membrane with 1% PIDH loading (TR-1.0%) achieved the highest ideal selectivities, with H 2 /N 2 = 20.95, O 2 /N 2 = 3.92, and CO 2 /N 2 = 25.10. Importantly, the CO 2 /N 2 separation performance of TR-1.0% and TR-2.0% nearly reached the 2008 Robeson upper bound. Overall, PIDH can effectively regulate the microstructure of TR membranes, improve their gas separation performance and antiaging ability, and thus provide a feasible chemical modification strategy for conventional PI and TR membrane materials.