Ultra‐Highly Stiff and Tough Shape Memory Polyurea with Unprecedented Energy Density by Precise Slight Cross‐Linking

Abstract Shape memory polymers (SMPs) have attracted significant attention and hold vast potential for diverse applications. Nevertheless, conventional SMPs suffer from notable shortcomings in terms of mechanical properties, environmental stability, and energy density, significantly constraining their practical utility. Here, inspired by the structure of muscle fibers, an innovative approach that involves the precise incorporation of subtle, permanent cross‐linking within a hierarchical hydrogen bonding supramolecular network is reported. This novel strategy has culminated in the development of covalent and supramolecular shape memory polyurea, which exhibits exceptional mechanical properties, including high stiffness (1347 MPa), strength (82.4 MPa), and toughness (312.7 MJ m −3 ), ensuring its suitability for a wide range of applications. Furthermore, it boasts remarkable recyclability and repairability, along with excellent resistance to moisture, heat, and solvents. Moreover, the polymer demonstrates outstanding shape memory effects characterized by a high energy density (24.5 MJ m −3 ), facilitated by the formation of strain‐induced oriented nanostructures that can store substantial amounts of entropic energy. Simultaneously, it maintains a remarkable 96% shape fixity and 99% shape recovery. This delicate interplay of covalent and supramolecular bonds opens up a promising pathway to the creation of high‐performance SMPs, expanding their applicability across various domains.