Solution‐Processable, Ladder‐Branched Polyimides of Intrinsic Microporosity by [4+4] Cycloaddition for Membrane Gas Separation

Advancements in membrane-based gas separation have the potential to address global challenges related to energy and the environment. However, new membrane materials must have excellent separation performance, stability, and processability, and simultaneously achieving all three metrics is extremely challenging. To circumvent these issues, a post-synthetic modification of polyimides of intrinsic microporosity (PIM-PIs) synthesized with a UV light (UV)-reactive anthracene co-monomer is reported. UV irradiation on the PIM-PI solution converts the anthracene units into dianthracene linkages by [4+4] cycloaddition, while the resultant PIM-PI is still solution-processable due to the branched structure. The ladder-like dianthracene moieties significantly increased both microporosity (<20 Å) and ultramicroporosity (<7 Å) of the precursor PIM-PI. Notably, the UV-treated PIM-PI membrane exhibits a large boost in pure-gas CO₂ permeability by up to 260%, reaching 376 barrer, while maintaining CO₂/CH₄ ideal selectivity of 35 at 1 bar. Moreover, the developed membrane material has enhanced stability against physical aging and plasticization and showcases excellent CO₂/CH₄ mixed-gas selectivity (>30 up to 31 bar feed pressure), which surpasses the 2018 mixed-gas upper bound.