Microporous polyimide networks with tunable micropore size constructed through side-chain engineering of linear precursors

Abstract

Microporous polyimides (MPIs) have been acted a significant role in porous organic polymers (POPs) for gas capture and separation. However, the MPIs are mostly constructed from monomers with rigid 3D or twisted structures or hyperbranched precursors, and their porous structure is mainly tuned by changing the length of the constructed units. Herein, the cross-linkable linear PIs with flexible skeletons are selected as precursors to construct the cross-linked microporous polyimides (C-MPIs). The method has significant comparative advantages including abundant monomers, the convenience of synthesis, cost-effectiveness, structural diversity and designability. Moreover, the micropore size of the C-MPIs (6FA-PE-CL, 6FA-PEPH-CL) can be tuned from 0.64 nm to 0.57 nm through the side-chain engineering of the cross-linkable linear PI precursors. The BET surface area of the C-MPIs are ranging from 635 to 698 m 2 g -1 and is among the best results for the reported linear MPIs. The smaller pore size (0.57 nm), higher micropore surface area (378 m 2 g -1 ) and micropore volume (0.17 cm 3 g -1 ) endow 6FA-PE-CL with better CO 2 selective uptake capacity (8.9 wt% and 58) than those of 6FA-PEPH-CL (7.3 wt% and 38). This work provides a side-chain engineering method to tune the pore structure of MPIs, which has tremendous potential for constructing high-performance polymer networks with abundant ultramicroporous structure (<0.7 nm) based on flexible linear polymers. Microporous polymer networks with tunable micropore sizes have been constructed through the side-chain engineering of cross-linkable linear polyimide precursors. • The microporous polymer networks with abundant ultramicropores were constructed from flexible linear polyimides. • The pore size can be finely tuned through the side-chain engineering method. • The microporous polyimide with a smaller pore size exhibits better CO 2 selective uptake capacity.