Tuning Gas‐Diffusion through Dynameric Membranes: Toward Rubbery Organic Frameworks (ROFs)

Abstract

AbstractObtaining high permeability whilst keeping a reasonable selectivity is the most important challenge in the development of membrane systems for gas separation. Satisfactory performance is usually obtained with polymeric membranes through which gas transport is controlled by gas‐diffusivity in glassy polymers and by gas‐solubility in rubbery polymers. During the last decade, important advances in this field have been made possible by molecular control of gas separation properties. The combination or replacement of classical glassy polymers with metal‐organic crystalline frameworks (crystalline MOFs), such as zeolitic imidazolate frameworks (ZIFs) or other zeolites, provides reasonable permeability through the porous networks formed, and high selectivity, due to so‐called ‘selectivity centers’, which interact specifically with the gas molecules. Despite impressive progress, difficulties in obtaining homogeneous, mechanically stable, thin layer MOFs on various supports have been encountered. Given the observed high permeabilities of rubbery polymers and their flexible casting properties, it should be very interesting to build rubbery organic frameworks (ROFs), as alternative materials for gas membrane separation systems. Here we use low macromolecular constituents and dialdehyde core connectors, in order to constitutionally generate ROFs. Distinct from rubbery polymeric membranes, the performance of the ROFs depends univocally on diffusional behaviors of gas molecules through the network. For all gases, a precise molecular composition of linear and star‐type macromonomers generates an optimal free volume for a maximal diffusion through the matrix. These results should initiate new interdisciplinary discussions about highly competitive systems for gas separation, which are constitutionally controlled on a molecular scale.