High-Selectivity CO₂ Mixture Separations by a Guanylated Polymer of Intrinsic Microporosity (PIM-G) Membrane

Membrane technology has the potential to replace thermal methods for gas separation, resulting in significant energy savings. However, materials with better combinations of permeability and selectivity are needed to fulfill industrial requirements. In this work, we functionalize a polymer of intrinsic microporosity with a high CO2 affinity guanidinium moiety to produce a highly CO2-permselective ionic polymer (PIM-G). Permeability–selectivity performance is compared under pure- and mixed-gas conditions for CO2/CH4, CO2/N2, and CO2/O2 gas pairs. In addition, counteranion identities are modified along the halide series (F–, Cl–, Br–, and I–) to optimize separation performance, with larger halides found to improve the CO2 permselectivity without a commensurate drop in the CO2 permeability.