Metal-Coordinated, Dual-Crosslinked PIM Polymer Membranes for Upgraded CO₂ Separation: Aging and Plasticization Resistance

The practical use of polymers of intrinsic microporosity (PIMs) in CO₂ separation is often hindered by their moderate selectivity, performance instability over time, and pressure constraints. To address these limitations, a straightforward approach is presented to enhance the CO₂ separation capability of PIM-1 by incorporating metal ions into uniformly hydrolyzed PIM-1 (cPIM). This dual linking strategy, achieved via ionic and coordination bonding of metal ions with the polymeric side chains including ─COOH and ─CONH₂, restructures the polymer, disrupting hydrogen bonds between cPIM chains and creating active sites for CO₂ via π-complexation. This modification enhances gas permeability while maintaining high selectivity. The optimized zinc-coordinated membrane achieves an impressive CO₂ permeability of ≈2,500 Barrer with CO₂/N₂ and CO₂/CH₄ selectivities of 27.1 and 23, respectively, outperforming pristine cPIM (700 Barrer; CO₂/N₂ = 27; CO₂/CH₄ = 19). Notably, this performance surpasses the 2008 Robeson upper-bound limits for both gas pairs. Additionally, the metal-coordinated membranes exhibit remarkable long-term stability, resisting aging effects for up to 20 days and maintaining anti-plasticization properties at pressures up to 20 bar. These dual-crosslinked membranes demonstrate promising potential for mixed gas separation, indicating their suitability for real-world industrial applications.