Sharon Lin

Polymers of intrinsic microporosity (PIMs) are traditionally formed from ladder backbones, but recent synthetic advances have allowed for the formation of non-traditional PIMs using a poly(ladder) motif, whereby rigid PIM-like sidechains are appended onto more flexible backbones. The effect of side-chain length on free volume and gas transport properties was recently evaluated for a methoxy-functionalized poly(ladder) (OMe-ROMP). In this study, we elaborate on the role of side-chain length and its influence on mixed-gas performance and plasticization stability for OMe-ROMP. Pure-gas sorption results are also reported, including hysteresis effects from CO2 conditioning. Taken together, this study reveals the role of side-chain length on gas sorption, diffusion, and plasticization for CO2/CH4 separations. We conclude that the length of a rigid side chain in the poly(ladder) motif is a valuable structural parameter to control sorption, diffusion, and stability towards plasticization for gas separation membrane materials.

Gas‐separation polymer membranes display a characteristic permeability–selectivity trade‐off that has limited their industrial use. The most comprehensive approach to improving performance is to devise strategies that simultaneously increase fractional free volume, narrow free volume distribution, and enhance sorption selectivity, but generalizable methods for such approaches are exceedingly rare. Here, we present an in situ crosslinking and solid‐state deprotection method to access previously inaccessible sorption and diffusion characteristics in amine‐functionalized polymers of intrinsic microporosity. Free volume element (FVE) size can be increased while preserving a narrow FVE distribution, enabling below‐upper bound polymers to surpass the H₂/N₂, H₂/CH₄, and O₂/N₂ upper bounds and improving CO₂‐based selectivities by 200 %. This approach can transform polymers into chemical analogues with improved performance, thereby overcoming traditional permeability–selectivity trade‐offs.

Gas‐separation polymer membranes display a characteristic permeability–selectivity trade‐off that has limited their industrial use. The most comprehensive approach to improving performance is to devise strategies that simultaneously increase fractional free volume, narrow free volume distribution, and enhance sorption selectivity, but generalizable methods for such approaches are exceedingly rare. Here, we present an in situ crosslinking and solid‐state deprotection method to access previously inaccessible sorption and diffusion characteristics in amine‐functionalized polymers of intrinsic microporosity. Free volume element (FVE) size can be increased while preserving a narrow FVE distribution, enabling below‐upper bound polymers to surpass the H₂/N₂, H₂/CH₄, and O₂/N₂ upper bounds and improving CO₂‐based selectivities by 200 %. This approach can transform polymers into chemical analogues with improved performance, thereby overcoming traditional permeability–selectivity trade‐offs.

Metal–organic frameworks (MOFs) represent the largest known class of porous crystalline materials ever synthesized. Their narrow pore windows and nearly unlimited structural and chemical features have made these materials of significant interest for membrane-based gas separations. In this comprehensive review, we discuss opportunities and challenges related to the formation of pure MOF films and mixed-matrix membranes (MMMs). Common and emerging separation applications are identified, and membrane transport theory for MOFs is described and contextualized relative to the governing principles that describe transport in polymers. Additionally, cross-cutting research opportunities using advanced metrologies and computational techniques are reviewed. To quantify membrane performance, we introduce a simple membrane performance score that has been tabulated for all of the literature data compiled in this review. These data are reported on upper bound plots, revealing classes of MOF materials that consistently demonstrate promising separation performance. Recommendations are provided with the intent of identifying the most promising materials and directions for the field in terms of fundamental science and eventual deployment of MOF materials for commercial membrane-based gas separations.