(709e) PEO-Based Semi-Interpenetrating Polymer Networks (S-IPNs) for CO2-Selective Membranes

PEO-based membranes are attractive for CO₂-related gas separations due to their high selectivity towards CO₂. However, PEO-rich membranes are frequently challenged by weak mechanical properties and a high crystallization tendency of PEO that hinders gas transport. While crosslinked PEO membranes represent an effective strategy to address these issues, their limited mechanical and thermal stability are still not satisfactory for some practical applications. In this talk, we report a new design strategy of semi-interpenetrating polymer networks (S-IPNs) that are fabricated from linear polyimides entwined by crosslinked PEO network to address abovementioned issues. This type of network structure can synergistically combine the mechanical properties of glassy polyimides with the excellent CO₂ separation ability of crosslinked PEO. Specifically, these new S-IPNs are consisted of crosslinked networks of Jeffamine^® polyetheramines penetrated by triptycene-containing linear (co)polyimides. In all, six unique S-IPNs were produced in various network-polyimide combinations to systematically investigate the dependence of membrane properties on the composition and membrane morphology. In particular, the PEO networks are varied in crosslink density, and the linear polyimides used include homopolyimide and PEO-co-polyimide copolymers of varied PEO content. Tested S-IPNs showed significantly improved mechanical properties relative to crosslinked pure PEO membranes. For example, the tensile strength of the low crosslink density S-IPN incorporating the homopolyimide improved by around 600%. Moreover, all S-IPNs featured greatly improved CO₂ permeability (up to 25-fold) as well as improved CO₂/H₂ and CO₂/N₂ selectivity compared to their counterpart homopolyimides and copolyimides, which place S-IPNs’ separation performance approaching and surpassing the 2008 Robeson upper bound for CO₂/H₂ and closely approaching the CO₂/N₂ upper bound. Given the same overall PEO content, S-IPNs consisted of linear copolyimides with moderate PEO content and PEO network of low crosslink density showed the best separation performance, suggesting the formation of the most desired membrane morphology in regards to PEO domain connectivity for selective and fast CO₂ transport. In this talk, the synthesis, fabrication and characterization of these new S-IPN membranes will be presented. Discussions will be focused on relating variations in microscopic structures (linear polyimide composition, crosslink density, and phase compatibility) with macroscopic physical and transport properties.