Flexible Crown‐Ether Polyimides Break the K ⁺ /Na ⁺ Selectivity Barrier in Artificial K ⁺ Channels

Natural potassium channels such as KcsA exhibit extraordinary K⁺/Na⁺ selectivity (>1000), whereas the best biomimetic counterparts have reached only 41.3. To close this performance gap, we developed a modular design comprising three tunable components: a flexible aliphatic polyimide (PI) backbone, variable alkyl linkers (C_nH_2n+1, n = 4-16), and ion-binding 18-crown-6 units. This architecture promotes robust membrane integration via the PI scaffold and precise control of crown ether conformation and spatial arrangement through linker optimization, enabling exceptionally selective and efficient K⁺ transport. Of four synthesized polymer channels, three display high K⁺ conductance (36.8-47.0 pS) -up to twice that of gramicidin A (23.2 pS) -together with K⁺/Na⁺ selectivity exceeding 100. Notably, channel 4, incorporating the longest C₁₆H₃₃ linker, achieves an unprecedented selectivity of 153.2 ± 5.3. This synergistic combination of ultrahigh selectivity and superior conductance establishes a new benchmark for artificial potassium channels and provides a versatile platform for biomimetic membrane technologies, channel-targeted therapeutics, and biosensing applications.