Fine-tuning gas separation performance of PIMs by engineering the novel tetrafluorinated monomers with aryl Schiff base units

Polymers of intrinsic microporosity (PIMs), as extremely promising materials for gas separation membranes, it is crucial to deeply investigate the relationship between their structures and properties. However, current efforts in PIMs structural development focus primarily on screening tetraphenol monomers with suitable contorted units, while systematic studies on the precise structural design of tetrafluorinated monomers and the corresponding structure-property relationships of the resulting PIMs remain scarce. In this study, a novel tetrafluorinated monomer featuring Schiff base units, namely 2,3,6,7-tetrafluoro-N9,N10-diphenylanthracene-9,10-diimine (TFNAD), was synthesized. A series of its derivatives with substituents of different sizes and positions (ortho-methyl, meta-methyl, meta-trifluoromethyl) was also developed. These monomers were then copolymerized with TTSBI and TFTPN to prepare a series of PIM-TFNAD-X copolymers. The influence of the substituents on the chain packing behavior, BET surface area, and pore size distribution of this series was systematically investigated, thereby revealing their impact on gas separation performance and physical aging behavior. Notably, the ortho-methyl substituted polymer (PIM-TFNAD-oMe), benefiting from the effect of the methyl in effectively disrupting the dense packing of polymer chains and restricting C-N bond rotation, significantly enhanced gas permeability while simultaneously maintaining selectivity, overcoming the permeability-selectivity trade-off to some extent. Furthermore, the separation performance of PIM-TFNAD-X was also evaluated under 15/85 CO 2 /N 2 mixed-gas conditions. This study not only introduces structurally tunable novel tetrafluorinated monomers to enrich the PIMs material library but also offers new insights into understanding their structure-property relationships.