Conjugation-Interrupted Polyimides with Amplified Local Electric Fields for SF6/N2 Separation

Abstract

Efficient capture of sulfur hexafluoride (SF6) is challenged by the molecule's chemical inertness and the persistent trade-off between adsorption capacity and selectivity in porous materials. Herein, we report a series of semi-cycloaliphatic microporous polyimides (MCPIs) via a "conjugation interruption" strategy that synergizes steric confinement with electrostatic modulation. By incorporating bicyclo[2.2.2]oct-7-ene (BCO) units into the polymer backbone, we effectively disrupt globalπ-electron delocalization. Density functional theory calculations show this interruption localizes electron density onto the imide carbonyls, thereby amplifying the local electric field (LEF). This intensified LEF, acting in concert with BCO-directed ultramicropores (~6.1 Å), creates high-affinity "electro-inductive traps" for SF6. Consequently, MCPI-1 exhibits a high SF6/N2 selectivity of 140 and an SF6 uptake of 1.69 mmol·g-1 at 273 K and 100 kPa. These findings highlight that modulating electron localization via backbone conjugation breaking provides a precise molecular engineering dimension to transcend the limitations of conventional aromatic frameworks.