Ultra-Strong, Crack-Tolerant Elastomers via Geometrically Confined H-Bonding Semicarbazides

The development of high-performance elastomers demands a combination of high tensile strength and toughness, yet overcoming the inherent trade-off between them remains a persistent challenge. Herein, inspired by the dense hydrogen-bonding assembly in spider silk, we developed a new generation of semicarbazide chain extender bearing high-density hydrogen-bonding sites for synthesizing poly(urethane-urea) (PUU). The geometric confinement, achieved by employing two specific semicarbazide chain extenders, is key to enhancing the material's properties. The resulting elastomer (PUU-HI) exhibits a nanoscale-ordered phase-separated structure and maximized H-bonding, which collectively amplify the supramolecular interactions and lead to ultra-robust mechanical performance. This material achieved a high tensile strength of 120.2 MPa, with toughness of 400.5 MJ m⁻³ and true fracture stress of 1.3 GPa, even surpassing those of spider silk. Molecular dynamics simulations revealed that geometric confinement effect enhances H-bonding interactions in PUU-HI. Multidimensional solid-state NMR demonstrates that this molecular packing confines chain mobility via augmented steric hindrance, facilitating orderly hard-domain stacking and efficient energy dissipation. The architecture additionally delivers exceptional crack tolerance, fatigue resistance, and recyclability. By designing novel H-bonding motifs and amplifying supramolecular interactions via geometric confinement, this work offers a promising strategy for developing mechanically robust and durable elastomers.