A Cation‐Methylene‐Phenyl Sequence Encodes Programmable Poly(Ionic Liquid) Coacervation and Robust Underwater Adhesion

Abstract Appropriate deciphering and translation of sequence‐dependent function in proteins is inspired by the cation–π interaction that is increasingly implicated in marine adhesives and membraneless organelles. A simplified cation‐methylene‐phenyl (C‐M‐P) sequence which enables triggerable poly(ionic liquid) coacervation is reported for the first time. Synthesis of the C‐M‐P structure motif requires only a one‐step quaternization, which is facile compared to the linear sequence of distinct repeating units in model proteins and sequence‐controlled polymers. The C‐M‐P code confers modular coacervation and advanced wet adhesion to task‐specific copolymers. It allows for exceptional underwater adhesion to various submerged substrates including glass (≈1 MPa) and porcine skins (140 KPa), paving the way for prospective adhesive applications in physiological saline and underwater marine salvage. This work introduces a powerful code that, in addition to combining the advantageous adaptive adhesive and phase properties of proteins, reduces the complexity in sequence design for programmable coacervates.