Stiff yet Tough, Moisture‐Tolerant, Room Temperature Self‐Healing and Thermoconductive Biomimetic Nanocomposites

Abstract Stiff yet room‐temperature self‐healing polymers are designed using molecularly engineered hydrogen bonds (H‐bonds). However, they often suffer from high brittleness, moisture sensitivity, and limited functionality. To overcome these challenges, high‐performance biomimetic nanocomposites inspired by inverse nacre structures are developed. A layered boron nitride nanosheet (BNNSs) skeleton is embedded within a previously synthesized room‐temperature self‐healing glassy polyurethane network, leveraging a solvent exchange‐induced self‐assembly strategy. This approach resolved the problem of BNNSs agglomeration and reconstructed robust yet dynamic noncovalent interfacial interactions, maximizing the reinforcing and toughening effects of BNNSs. Consequently, the nanocomposite exhibited significant mechanical enhancements, including 6.6‐fold, 14.4‐fold, 490‐fold, and 35.7‐fold increases in flexural modulus, strength, toughness, and fracture toughness, respectively, achieving a balance between stiffness and toughness. Furthermore, the nanocomposite retained room‐temperature self‐healing properties through the secondary relaxation of H‐bonds. The impermeability of BNNSs effectively shielded H‐bonds from moisture, fundamentally altering the hygroscopic nature of self‐healing glassy polyurethanes. Additionally, the highly oriented and interconnected BNNSs skeleton endowed the nanocomposite with an in‐plane thermal conductivity of up to 11.54 W m ⁻¹ K ⁻¹ , making it a promising candidate for next‐generation high‐performance intelligent thermal interface materials.