Citric Acid‐Mediated Liquid–Liquid Phase Separation of Polyphenol‐Polyethylene Glycol for Tough Adhesives

ABSTRACT Adhesives are essential in diverse industrial fields, and bioadhesives play a critical role in medicine for minimally invasive tissue repair and device integration. However, existing systems, particularly polyethylene glycol (PEG)‐based adhesives, often suffer from brittleness, inadequate performance under extreme temperatures, and limited substrate versatility. To overcome these challenges, we developed a novel polyphenol‐PEG adhesive platform through citric acid (CA)‐mediated liquid–liquid phase separation (LLPS). This process, driven by CA‐regulated hydrogen bonding as confirmed by XPS, FTIR, UV spectroscopy, and solution studies, produces adhesives with exceptional properties: peel strength near 15 N/cm, shear strength exceeding 4 MPa on hydrophilic substrates, rapid adhesion within 10 s, and operational stability from liquid nitrogen temperatures up to about 150°C, maintaining over 1 MPa shear strength at 200°C exposure. The adhesive demonstrates effective sealing of fractured bone, adhering to wet biological tissues and serving as an eco‐friendly solution for restoring cultural artifacts. This study establishes the condensate formed by the CA‐regulated LLPS process in the polyphenol‐PEG system as a novel, ultra‐robust adhesive suitable for demanding biomedical and industrial applications.