(750f) Super-Rigid, Intrinsically Microporous Ladder Polymers for Enhanced Gas Separation Performance and Physical Aging Resistance

High-free-volume glassy polymers such as PIM-1 have shown exceptional promise for advancing current gas separation membrane technology. However, high-free-volume polymers are often limited by severe declines in permeability over time due to reductions in their largely conformation-based free volume from the densification that occurs during physical aging. Here, we present an innovative macromolecular design of ladder-like copolymers that exploit the unique molecular architecture of pentiptycene as building blocks for non-collapsible, yet tunable, configuration-based free volume microporosity. The structural hierarchy of the pentiptycene unit imbues a more permanent, intrinsic free volume into the polymer for increased size sieving while providing a versatile framework that allows tunable ultra-microporosity. Monomers utilizing different shapes of the pentiptycene framework (i.e., S- or C-shaped) were synthesized with tailorable substituent groups and incorporated into copolymers with PIM-1 to study the effect of configurational free volume on gas transport. Achieved copolymers have shown remarkable potential as gas separation membranes, surpassing the 2008 upper bound for several gas pairs. For example, incorporation of 33 mol % of the S-shaped pentiptycene unit provided exceptional combinations of permeability and selectivity for O₂/N₂, with an O₂ permeability of 2370 Barrer and an O₂/N₂ selectivity of 4.6. Additionally, a thin film integrated with only 17 mol % of the C-shaped pentiptycene unit had a hydrogen permeability of 5900 Barrer with upper bound selectivities for typical hydrogen-based separations (i.e., 𝛼(H₂/CH₄) = 4.9; 𝛼(H₂/N₂) = 7.7). A preliminary aging study showed that the 17 mol % C-shape polymer had 30% increases in permeability across all gases after aging 120 days, while maintaining selectivity. This is in sharp contrast to existing ladder polymers like PIM-1 which show significant decreases in permeability over short periods of time due to physical aging. Permeation testing of CO₂/CH₄ in a 50:50 feed ratio was performed within the polymer series and showed surprising mixed-gas separation performance, with the 33 mol % S-shaped copolymer displaying a CO₂ permeability of 2700 Barrer with a CO₂/CH₄ selectivity of 16.6. In this talk, synthesis and characterization of these new ladder copolymers will be presented. Discussions will focus on elucidating the fundamental structure-property relationships within the polymer series.