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

Mengtao Wang,Luxin Sun,Chen Luo,Jiachen Chu,Congcong Wu,Kunying Li,Xuepeng Li,Kai Song,Jianxin Li,Xiaohua Ma

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.