In Situ Formation of Tröger’s Base-Derived Porous Organic Polymer Membranes with Greatly Enhanced Ultramicroporosity and Gas Separation Property

Formation of porous organic polymer (POP) membranes is a great challenge due to their highly cross-linked nature that prevents film formability. Here, we reported a series of mechanically strong POP membranes derived from a cross-linked Tröger’s base using 3,3′-dimethylbiphenyl-4,4′-diamine as a linear monomer and 1,3,5-tris(4-aminophenyl)benzene (TPB) as a cross-linking node. As the TPB content increased from 0% (TPB-0) to 75% (TPB-75), these POP membranes show a continuously decreased chain spacing from 7.96 to 6.22 Å, increased Brunauer–Emmet–Teller surface areas from 250 to 531 m2 g–1, and enhanced ultramicropore volumes from 0.046 to 0.143 cm3. Thereby, a huge increase in permeability without sacrificing selectivity was observed for these TPB-based POP membranes. For example, TPB-75 exhibited not only over 19 times larger O2 permeability (790 vs 50.3 Barrer) but also slightly higher O2/N2 selectivity (4.8 vs 4.5) than the linear TPB-0. The overall separation performances quickly improved from below the 2008 trade-off curves for TPB-0 to near the latest 2015 curves for O2/N2, H2/N2, and H2/CH4 as the TPB content increased. These results are attributed to the significantly improved ultramicroporosity that enhanced the molecular sieving effect by the POP structure induced by in situ cross-linking. This design protocol and the POP membranes provide a novel direction for advanced gas separation membranes.