Resolving the Strength–Modulus–Elasticity Tradeoff in Elastomers Using Dual Phase‐Separated Nanodomains

ABSTRACT Achieving elastomers that simultaneously combine ultrahigh strength, high modulus, and excellent elasticity remains a longstanding challenge because these properties are intrinsically conflicting. Here, we report a dual phase‐separated nanodomain strategy that resolves this trade‐off by transforming reversible cross‐links into spatially confined reinforcing nanodomains. Elastomers are fabricated via copolymerization of rigid aromatic polyurea segments with flexible poly(urethane‐urea) chains containing acylsemicarbazide moieties. The resulting elastomers exhibit an exceptional combination of mechanical properties, including tensile strength of 104.6 MPa, Young's modulus of 43.1 MPa, toughness of 350 MJ m −3 , and full recovery after 600% strain. Small‐angle x‐ray scattering and electron microscopy reveal two distinct nanodomains originating from self‐assembled aromatic polyurea segments and acylsemicarbazide‐stacked hydrogen‐bond arrays, respectively. Their synergistic reinforcement increases matrix rigidity while preserving entropy elasticity, enabling the simultaneous realization of ultrahigh mechanical robustness and excellent elastic recovery. The elastomers further demonstrate outstanding puncture resistance, environmental stability, healability, and reprocessability. When used as binders for carbon‐fiber fabrics, the composites achieve record‐high fracture energies of up to 2059 kJ m −2 , owing to the exceptional mechanical robustness and energy dissipation of the elastomer, together with strong elastomer‐fiber interfacial adhesion. This dual nanodomain design provides a novel route to high‐performance elastomers that transcend conventional strength‐modulus‐elasticity trade‐offs.