Tailoring polymers for ultramicroporosity is key to achieving fast and size-selective gas separations. Functionalized polymers of intrinsic microporosity (PIMs) can act as reactive microporous scaffolds for the insertion of organic macrocyclic supramolecules with precise cavities to provide a new platform for ultramicroporous polymer membrane design. Through the solid-state proton-transfer interactions of functionalized PIM-1 membranes with solutions of calixarene molecules, large microporous regions within the membranes can be effectively transformed into a network of size-sieving cavities. Positronium annihilation lifetime spectroscopy (PALS) reveals the emergence of a sharper ultramicropore distribution. As a result, membranes inserted with calixarenes of different sizes show dramatically increased selectivity for several size-discriminative gas pairs, including H2/N2, H2/CH4, O2/N2, N2/CH4 and CO2/CH4, with only mildly reduced permeabilities. Their separation performances are able to surpass the respective state-of-the-art upper bounds. These membranes also demonstrate surprising C2H4/C2H6 separation properties that can reach the metrics of carbon molecular sieve membranes. Most attractively, the micropore-insertion of supramolecules does not cause any weakening to the chain entanglement of PIM-1, allowing the reacted membranes to remain as robust and flexible polymeric films almost perfectly, which is critical for scalable thin-film fabrication. The approach presented here offers a versatile materials toolbox for making ultra-selective PIM membranes.
