Thermal Debromination-Induced Cross-Linking of PIM-Polyimide Membranes: Improved CO2 Gas Permeability, Selectivity, and Separation Performance

Demand for advanced polymers with intrinsic microporosity (PIM) is growing due to their enhanced free volume and potential in gas separation membranes. However, PIM-based membranes are vulnerable to aging effects and loss of stable performance. To overcome this drawback, we synthesized a PIM-polyimide (PI) polymer based on PIM-dianhydride and a durene diamine unit (PIM-PI-1). Bromination at the PIM-PI-1 benzyl positions provided PIM-PI-Br-Z (bromination degree Z = 15, 25, and 50 %), precursors for thermal debromination-induced crosslinking. The optimal cross-linked membrane derived from 50 % brominated PIM-PI-Br-50 demonstrated remarkable CO2 permeability (5401 Barrer) combined with good CO2/CH4 (21.1) and CO2/N2 (21.0) selectivity, surpassing the 2008 upper bound. Additionally, the membrane demonstrated good performance in mixed gas tests (CO2/N2), exhibiting a CO2 permeability of 2299 Barrer and CO2/N2 selectivity of 31. The thermally crosslinked membrane exhibited promising anti-aging properties up to 13 days and excellent CO2-induced plasticization resistance even under pressures up to 18 atm, demonstrating its potential for high-performance PIM-based gas separation membranes.