A New Design Strategy of Schiff‐Base Cage Structure for Exceptional Strength‐Toughness Waterborne Polyurethanes Toward Application in Infrared Stealth

To address the escalating industrial demands for high-performance polymers with both superior strength and toughness, a unique boronic acid imine cage (BIC) compound containing a Schiff-base structure is innovatively synthesized and covalently incorporated into the molecular chains of waterborne polyurethanes to obtain the elastomers (DWPU-BIC-x) with outstanding strength, toughness, tear resistance, and fatigue resistance. In-depth mechanism analysis reveals that BIC functions as a "structural hub", leveraging its rigid cage-like geometry and high-density interaction sites (aromatic rings for π-π stacking and nitrogen atoms for hydrogen bonding) to modulate molecular chain movement and intermolecular forces, thereby facilitating efficient energy dissipation under mechanical stress. The optimized material achieves an outstanding strength (53.0 MPa) at a high break elongation (1095.5%) and an impressive toughness (269.8 MJ m^-3), which shows that this structural design strategy successfully breaks the traditional strength-toughness trade-off in polymers. Furthermore, the investigation regarding the infrared stealth performances of the elastomers produced by the coordination of ─C═N─ in BIC with various metal ions demonstrates the material resulting after coordinating with Sm³⁺ with good infrared stealth capability. The work not only provides a novel design of high-performance polyurethane materials but also advances the development of infrared stealth technology.