Ultra‐Tough Single‐Network Hydrogels via the Synergy of Defect Elimination and Dual Crosslinking

Abstract Network imperfections, such as multi‐dispersed junctions and dangling chains, significantly impair the mechanical performance of hydrogels and elastomers synthesized via free radical reactions (FRRs). Great efforts have been made to introduce sacrificial structures to enhance toughness but cause pronounced hysteresis, leaving a comprehensive solution elusive. Herein, a class of robust single‐network hydrogels with minimal imperfections is reported by employing nano‐crosslinkers and nano‐initiators to produce monodispersed crosslinking points and eliminate dangling‐chain defects, in the formation of dual crosslinking of thiolate‐Au bond and chemically covalent bond in the network. As a result, the hydrogel achieves a maximum fracture toughness (78 500 J m −2 ) and fatigue resistance (2480 J m −2 ), with over 13 and 55 fold increases attributed to the incorporation of dangling chains and dual crosslinking, respectively, without compromising its low hysteresis (0.07). Eliminating dangling chains also improves interfacial contact and osmotic pressure resistance, enabling exceptional underwater self‐healing and swelling properties. Even with a high water‐uptake of up to 95 wt.%, the swollen hydrogel exhibits stretchability exceeding 2000%, without obvious mechanical degradation after one month of water incubation. This work demonstrates a model system for developing resilient polymers with minimized imperfections derived from FRRs, showing numerous potential applications in underwater applications.