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Abstract Porous organic cages (POCs) represent a new class of microporous materials with an impressive breadth of potential applications. One of their many advantages is the degree of tunability of cage properties, similar to that seen in more established microporous materials like metal‐organic frameworks. In this work, a prototypical POC, CC3, is used to explore the potential to tune cage properties via post‐synthetic dynamic covalent chemistry. Ethylenediamine, the linker used in another POC, CC1, was partially substituted into the CC3 cage structure to varying degrees based on the starting relative molar ratios. The resulting products were investigated for the relative distribution of the two linkers, crystallinity, and surface area. It was found that even when small amounts of other compatible diamine linkers are introduced, they substitute into the existing cages, although some structural products are apparently favored over others within the reactant ratios investigated. 

In membrane-based separation, molecular size differences relative to membrane pore sizes govern mass flux and separation efficiency. In applications requiring complex molecular differentiation, such as in natural gas processing, cascaded pore size distributions in membranes allow different permeate molecules to be separated without a reduction in throughput. Here, we report the decoration of microporous polymer membrane surfaces with molecular fluorine. Molecular fluorine penetrates through the microporous interface and reacts with rigid polymeric backbones, resulting in membrane micropores with multimodal pore size distributions. The fluorine acts as angstrom-scale apertures that can be controlled for molecular transport. We achieved a highly effective gas separation performance in several industrially relevant hollow-fibrous modular platform with stable responses over 1 year.