Preparation of high-performance polyimide membranes for gas separation via thermal rearrangement and cyano-induced thermal crosslinking

Polyimide (PI) gas separation membranes have long faced the challenge of inherent "trade-off" effect between gas permeability and selectivity, which severely hinders their large-scale application. In this study, the balance between gas permeability and selectivity was finely tuned through the combination of thermal rearrangement and cyano-induced thermal crosslinking, where a novel post-grafting modification method was employed to quantitatively introduce cyano groups onto hydroxyl-containing PI, followed by thermal treatment. Through the grafting content regulation, the resulting PI membranes achieved a pure CO 2 permeability of 500.65 Barrer and a CO 2 /CH 4 ideal selectivity of 39.58, surpassing the 2008 Robeson upper bound and exhibiting rapid gas sieving characteristics. Moreover, the CO 2 /CH 4 mixed-gas separation performance of the membrane was also remarkable, exceeding the 2018 CO 2 /CH 4 mixed-gas upper bound. This study proposes a "two-birds-one-stone" strategy that simultaneously addresses the challenges of the "trade-off" effect as well as plasticization and aging resistance in PI membranes, providing a new general strategy for the development of highly efficient PI-based membrane materials.