Ultramicropore‐Matched Molecular Transport in Low‐Loading Mixed‐Matrix Membranes via Trace‐Oxygen‐Mediated Thermal Reorganization

ABSTRACT The complementary structural tunability of polymers of intrinsic microporosity (PIMs) and metal–organic frameworks (MOFs) redefines the design space for engineering precise transport channels in mixed‐matrix membranes (MMMs). Herein, we present that trace‐oxygen‐mediated thermal reorganization (TOTR) of PIM‐1 micropores enables MOF‐dominated gas transport in MMMs without requiring high filler loading. Spectroscopic analyses and molecular simulations reveal trace‐oxygen‐mediated radical processes that induce the PIM‐1 backbone rearrangement, together with triazine crosslinking and partial π‐conjugation extension, resulting in a contracted and homogenized ultramicropore distribution. Meanwhile, the dual‐interface design establishes a covalently coupled MOF–polymer interface, where the interfacial carboxylated PIM‐1 (cPIM‐1) layer co‐reorganizes with the polymer matrix to form an integrated microporous environment with suppressed defects and enhanced mechanical robustness. This coupled pore‐and‐interface regulation integrates PIM‐1 ultramicropores and MOF micropores into pore‐matched transport channels, enabling effective expression of MOF sieving capability at an ultralow filler loading of 2 wt.%. The resulting MMMs deliver approximately threefold enhancement in CO 2 /CH 4 and CO 2 /N 2 selectivity compared with PIM‐1 membranes, while maintaining high CO 2 permeability and improved resistance to physical aging and plasticization. This study may broaden the design concepts for advanced MMMs toward challenging molecular separations.