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Penetrant-induced plasticization has prevented the industrial deployment of many polymers for membrane-based gas separations. With the advent of microporous polymers, new structural design features and unprecedented property sets are now accessible under controlled laboratory conditions, but property sets can often deteriorate due to plasticization. Therefore, a critical understanding of the origins of plasticization in microporous polymers and the development of strategies to mitigate this effect are needed to advance this area of research. Herein, an integrative discussion is provided on seminal plasticization theory and gas transport models, and these theories and models are compared to an exhaustive database of plasticization characteristics of microporous polymers. Correlations between specific polymer properties and plasticization behavior are presented, including analyses of plasticization pressures from pure-gas permeation tests and mixed-gas permeation tests for pure polymers and composite films. Finally, an evaluation of common and current state-of-the-art strategies to mitigate plasticization is provided along with suggestions for future directions of fundamental and applied research on the topic. [ABSTRACT FROM AUTHOR]

Membrane‐based gas separations are crucial for an energy‐efficient future. However, it is difficult to develop membrane materials that are high‐performing, scalable, and processable. Microporous organic polymers (MOPs) combine benefits for gas sieving and solution processability. Herein, we report membrane performance for a new family of microporous poly(arylene ether)s (PAEs) synthesized via Pd‐catalyzed C−O coupling reactions. The scaffold of these microporous polymers consists of rigid three‐dimensional triptycene and stereocontorted spirobifluorene, endowing these polymers with micropore dimensions attractive for gas separations. This robust PAE synthesis method allows for the facile incorporation of functionalities and branched linkers for control of permeation and mechanical properties. A solution‐processable branched polymer was formed into a submicron film and characterized for permeance and selectivity, revealing lab data that rivals property sets of commercially available membranes already optimized for much thinner configurations. Moreover, the branching motif endows these materials with outstanding plasticization resistance, and their microporous structure and stability enables benefits from competitive sorption, increasing CO2/CH4 and (H2S+CO2)/CH4 selectivity in mixture tests as predicted by the dual‐mode sorption model. The structural tunability, stability, and ease‐of‐processing suggest that this new platform of microporous polymers provides generalizable design strategies to form MOPs at scale for demanding gas separations in industry. [ABSTRACT FROM AUTHOR]

Membrane‐based separations offer energy‐efficient solutions for various applications, but commercial polymer membranes show limited performance and stability. Mixed‐matrix membranes (MMMs), incorporating nanoporous inorganic materials in polymer matrices, have been of great interest to circumvent these polymer‐specific issues. However, reaching the percolation threshold is crucial to leverage high‐performing inorganic phases fully, yet the traditional sphere‐like nanofillers require high loadings that easily result in agglomerations and non‐selective defects. Here, a branch‐shaped zeolitic imidazole framework‐8 (ZIF‐8) nanoparticle is synthesized where its unique morphology automatically interconnects, readily forming percolated networks within the polymer matrix at loadings as low as 20 wt.%. Because of the high surface‐area‐to‐volume ratios of branched ZIF‐8 (BZ), strong polymer–particle interactions suppress polymer chain dynamics and the rotation of the ZIF‐8 ligand. This interphase confinement results in enhanced membrane stability and a smaller diffusion cut‐off than traditional ZIF‐8. With pre‐connected diffusion pathways and confined ZIF pores, BZ MMMs significantly outperformed MMMs with sphere‐like ZIF‐8 for H2‐based separations. Overall, the findings provide a novel approach to enhance filler effects in MMMs even at low loadings without any alignment, which can enable the development of advanced membranes in fields where percolation is desired, including separations, sensors, conductors, and batteries. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: Over the past three decades, polymeric gas separation membranes have become widely used for a variety of industrial gas separations applications. This review presents the fundamental scientific principles underpinning the operation of polymers for gas separations, including the solution-diffusion model and various structure/property relations, describes membrane fabrication technology, describes polymers believed to be used commercially for gas separations, and discusses some challenges associated with membrane materials development. A description of new classes of polymers being considered for gas separations, largely to overcome existing challenges or access applications that are not yet practiced commercially, is also provided. Some classes of polymers discussed in this review that have been the focus of much recent work include thermally rearranged (TR) polymers, polymers of intrinsic microporosity (PIMs), room-temperature ionic liquids (RTILs), perfluoropolymers, and high-performance polyimides. [Copyright &y& Elsevier]

Membrane separations has been increasingly recognized as a key technology platform for improving the energy efficiency of many separations processes. Likewise, additive manufacturing (AM), or 3-dimensional (3D) printing as it is often called, is a rapidly emergent technology platform for manufacturing in many industrial sectors. It has become increasingly common to marry these two platforms to take advantage of the additive nature of 3D printing with the increasing need for membrane technology that is adaptable to separations needs. Conventional membrane manufacturing approaches, such as casting, typically result in thick membranes that limit productivity and potentially waste material in a non-performing support layer. Interfacial polymerization (IP) offered a new vision for thin-film composite desalination membranes, yet it was limited to certain chemistries while exhibiting other drawbacks. Additive manufacturing offers certain benefits over these techniques to membranes, including the ability to expand the library of materials that can be processed while also offering a degree of customization that is impossible in conventional manufacturing. This review article evaluates an increasing body of literature on using printing to make membranes and considers the limitations and opportunities for printing to enhance existing membrane technology and expand the reach of membranes into other industries. We also provide a perspective from leading experts in membrane technology to see where there are opportunities to use printing in different membrane science disciplines. [Display omitted] • We provide a historical perspective of membrane manufacturing and its limitations. • We review the recent applications of additive manufacturing to membrane technology. • We compare 3D printing with conventional methods in terms of key manufacturing metrics. • Future challenges and perspectives of 3D printing on membrane technology are proposed. • The corresponding author has multiple pending patents on 3D printed membrane technology. [ABSTRACT FROM AUTHOR]

Fractional free volume (FFV) is a commonly used metric for the development of structure–property relationships for polymer membranes. The most common method to calculate FFV uses Bondi's group contribution method, first introduced in 1964. While updated in 1997, there has not been a significant compilation of new structural motifs since the advent of linear microporous polymers. In this study, we critically examined the assumptions in Bondi's original method and provide four recommendations to streamline and improve the accuracy of calculating van der Waals volume (V W) for any group. Using these recommendations, we created an updated list of V W values for structural groups commonly present in microporous polymers. The V W and FFV values were then calculated for a database of 123 microporous and high free volume polymers from the literature, showing an average 7% decrease in V W and corresponding increase in FFV by a factor of 24% when compared to prior group contribution correlations in the literature. The significant apparent increase in estimated FFV provides a new perspective to understand and interpret the role of free volume on the separation performance of linear microporous polymers. Additionally, standardization of the group contribution method allows for the direct comparison of FFV values across studies. [Display omitted] • Bondi's group contribution method to calculate fractional free volume (FFV) was refined. •An updated procedure to calculate van der Waals volume for any group is presented. •New FFV values were calculated for 123 polymers, including microporous polymers. •On average, new FFV values were greater than reported literature FFV by a factor of 24%. [ABSTRACT FROM AUTHOR]