[2.2]Paracyclophane-Based Polyimides of Intrinsic Microporosity for Gas Separation

Polyimides (PIs) are a significant class of high-performance polymers due to their exceptional thermal, mechanical, and chemical stability. Their combination with polymers of intrinsic microporosity (PIMs) provides access to materials with structural robustness coupled with permanent microporosity. Progress in this area is frequently constrained by the limited availability of difficult-to-prepare and structurally complex dianhydrides. Building on our recent work on [2.2]-paracyclophane (PCP)-based PIMs for gas sorption, we report a series of PCP-polyimide PIMs synthesized from PCP-derived dianhydrides and amino-PCP monomers. The preparation of these dianhydrides enabled a systematic investigation of the monomer structure and connectivity. Two polymer families were obtained: PCP-PIs incorporating pseudo-para and pseudo-meta-PCP units and an ethanoanthracene analogue and a corresponding series of 4,4'-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA)-based PCP polymers. Gas sorption measurements show very good CO₂/N₂ separation performance with the highest selectivity observed for the meta-PCP-ethanoanthracene system (PCP-PI4, ∼40). Polymers derived entirely from PCP-based dianhydride and bisaniline units in a pseudo-meta configuration also display a capability for strong separation of gases (CO₂/N₂ = 32.5), underscoring the role of monomer design in tuning the separation properties. Extensive structural and morphological characterizations were performed using multinuclear solid-state NMR, Fourier-transform infrared spectroscopy (FT-IR), wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX), while the thermal stability was determined by thermogravimetric analysis (TGA).