Reversibly Cross‐Linked Damage‐Tolerant Polymers Breaking the Strength–Stretchability Trade‐Off

ABSTRACT Polymers that combine exceptional stretchability with high mechanical robustness are essential for advanced applications. To ensure their reliability, it is critical to integrate damage tolerance, which suppresses crack propagation and prevents catastrophic failure under extreme deformation. However, overcoming the intrinsic trade‐off between stretchability and strength remains a formidable challenge in polymer science, particularly when damage tolerance is also required. Here, we show the scalable fabrication of super‐stretchable polymers exhibiting exceptional mechanical robustness and remarkable damage tolerance, achieved by cross‐linking soft polymer chains through synergistic urea‐based hydrogen bonding and hydrophobic interactions. These polymers exhibit record‐high elongations up to ∼100,000 times their original length while maintaining an extensional true stress of 35.0 MPa at a strain of 33.6, and an extraordinary fracture energy exceeding 374.8 kJ m −2 . The extreme stretchability of these polymers arises from the successive breakage, chain slippage, and reformation of noncovalent cross‐links. Meanwhile, mechanical robustness and pronounced strain hardening are sustained by a strain‐induced transition of urea hydrogen bonds from double to quadruple configurations, together with the progressive orientation of polymer chains. These reversibly cross‐linked polymers, featuring intrinsic self‐healing and reprocessability, open broad opportunities for extremely deformable polymer materials where robustness, reliability, and sustainability are paramount.