Direct Thermal Oxidative Cross-Linking in Air toward Hierarchically Microporous Polymer Membranes for Advanced Molecular Sieving

In situ thermal oxidative cross-linking provides an efficient strategy for manipulating microporosity in polymeric gas separation membranes. Herein, we report a rational macromolecular design combining microporous polymers with thermal oxidative cross-linking to fabricate highly permselective membranes for advanced energy-efficient gas separations. We demonstrate that direct thermal treatment in air induces both oxidative chain scission and thermal oxidative cross-linking, leading to a hierarchically microporous architecture enabling simultaneous enhancement of permeability and selectivity. Consequently, the TOC-PI-Trip-TB-450-30min membrane containing both the triptycene and Tröger's base moieties upon thermal treatment at 450 °C for 30 min in air exhibits H2 and CO2 permeabilities of 1138 and 640 Barrer, respectively, and H2/N2, H2/CH4, and CO2/CH4 selectivities of 76, 121, and 68, respectively, exceeding or approaching the state-of-the-art upper bounds. This study also confirmed that the microcavity characteristics and gas permeation performance of the thermal-oxidatively cross-linked membranes are highly tunable by regulating the polymer structure, oxidative temperature, and reaction time.