Intrinsically microporous polyimide membranes with synergistic aromatic and alicyclic linking groups for efficient molecular separation

Polymers of intrinsic microporosity (PIMs) are widely recognized for having great potential in reforming membrane technology for molecular separation within organic solvents, due to their rich and appropriate pore structures with a size < 2 nm. However, the swelling in organic solvents has a significant effect on their pore structures due to the amorphous and linear nature, resulting in the permeability and selectivity performances of developed PIM membranes being far from ideal. In this work, we synthesized an advanced polyimide of intrinsic microporosity by integrating a Tröger's base (TB) structure with an alternating structure of aromatic (naphthalenediimide, NDI) and alicyclic (bicyclooctenediimide, BCODI) linking groups. The TB with a rigid and twisted structure was used to furnish a basis for inhibiting chain packing for high overall free volume. The ultra-rigid NDI units maintained such a tailored high free volume and provided superior solvent resistance. The relatively flexible and polar BCODI units promoted local chain mobility to tailor uniform pore size distribution and increased affinity for polar solvents. The innovative design fostered the formation of stable, uniform, and highly solvent-accessible intrinsic micropores. The prepared TFC membrane exhibited good organic solvent separation capabilities, achieving an ethanol permeance of 7.6 L m-2h−1 bar−1 and a low molecular weight cut-off (MWCO) of approximately 470 Da. This work contributes significantly to the strategic design of PIMs for preparing high-performance membranes for realistic chemical-related separation application scenarios.