Microporous polymer networks constructed from cross-linkable linear polyimides for CO2 adsorption

In recent years, linear polyimides of intrinsic microporosity have been widely used in the field of gas adsorption and separation because of their high BET surface area and microporous structures. Most of the microporous structures come from the twisted main-chain structures in the linear polyimides of intrinsic microporosity. Therefore, most linear polyimides (PI) without twisted structure have no porosity. Herein, to construct the linear polyimide with microporous structure, a sequence of microporous polyimides (PIs-CL) were constructed from the flexible linear polyimide precursors through the thermal crosslinking reaction. The polyimide precursors without twisted structure were synthesized from a well-designed diamine TFVBPA with cross-linkable ethynyl groups and several commercial dianhydrides (ODPA, BPDA, PMDA and 6FDA) by polycondensation to research the influence of the main-chain structure on the porous characters. The introduction of crosslinked structures gives the linear crosslinked polyimides (PIs-CL) with porous structures. The PIs-CL show obviously improved porosity (0.52–1.71 nm) and higher BET surface area (337–618 m 2  g −1 ) than those of the uncrosslinked polyimides (PIs). Moreover, PIs-CL have favorable CO 2 adsorption (5.7–9.3 wt%) as well as good CO 2 /N 2 selectivity (34.4–58.5) at 273 K, which are better than other polyimides materials. The introduction of crosslinked structures is an effective way to improve microporous porosity and gas sorption performance.