Robust yet deformable nanodomains for super-strong and ultra-tough reversibly cross-linked plastics

High-performance plastics that simultaneously integrate exceptional strength, modulus, toughness and recyclability remain elusive owing to intrinsic property trade-offs. Here, we report super-strong and ultra-tough reversibly cross-linked poly(aryl amide)-polyurea (PA-PU) plastics obtained by copolymerizing rigid PA and flexible PU chains. <i>In situ</i>-formed hydrogen-bonded PU nanodomains act as robust yet deformable cross-links, reinforcing strength of the plastics while efficiently dissipating energy through nanodomain deformation and hydrogen-bond dissociation. As a result, the PA-PU plastics exhibit a tensile strength of 103.7 MPa, a Young's modulus of 2.5 GPa and a toughness of 36.1 MJ m^-3, along with satisfactory thermal resistance, chemical stability and re-processability. Incorporation with carbon fibers (CFs) produces PA-PU/CF composites with superior tensile and flexural properties, outstanding low-temperature impact resistance and solvent-assisted recyclability, outperforming conventional epoxy/CF composites. This work establishes that <i>in situ</i>-formed nanodomains combining mechanical robustness with deformability offer an effective strategy to toughen plastics.