Porous organic polymer membranes derived from tetramine-based Tröger's base with simultaneously enhanced permeability and selectivity

Combining the advantages of polymers of intrinsic microporosity (PIM) and porous organic polymer (POP) is a very promising method for achieving high-efficiency gas separation membranes. In this study, we successfully synthesized a series of novel POP membranes derived from a highly crosslinked Tröger's base (TB), using 3,3′-dimethylbiphenyl-4,4′-diamine as a linear part and 4,5-bis(4-aminophenyl)-[1,1:2,1-terphenyl]-4,4-diamine (TPDA) as crosslinker that contains four nodes. The resulting POP network membranes showed reduced interchain spacing from 7.96 to 5.76 Å, significantly increased Brunauer-Emmett-Teller (BET) surface area from 250 to 534 m² g⁻¹, and markedly enhanced ultramicroporosity from TPDA-0 to TPDA-100. Compared to the linear TPDA-0, the crosslinked membranes demonstrated marked improvement in gas permeability and gas pair selectivity. For example, the TPDA-100 exhibited ∼10 times higher O₂ permeability (507 vs. 50.3 Barrer) along with an improved O₂/N₂ selectivity (4.7 vs. 4.5) compared to the linear TPDA-0. With the increasing of TPDA content, the overall gas separation performance gradually increased from far below to surpass the 2008 Robeson Upper bound limits for O₂/N₂, H₂/N₂, and H₂/CH₄. These enhancements are attributed to the higher ultramicroporosity volume and concentration originated from the in-situ crosslinked POP structure. This direct synthesis strategy provides a promising and scalable strategy for developing high-performance gas separation membrane materials.