Mechanically Robust and Thermally Adaptive Solid–Solid Phase Change Materials Based on Dynamic Boron-Urethane Bond-Cross-Linked Polyurethane Networks

Solid–solid phase change materials (SSPCMs) have emerged as promising candidates for latent heat storage in thermal management applications. However, their practical application is often constrained by inferior mechanical strength, limited solvent resistance, and inadequate shape memory performance. To address these challenges, a series of polyurethane-based SSPCMs were designed and synthesized via quadruple boron-urethane bonds. In this system, polyethylene glycol (PEG6K, Mn = 6000 g/mol) served as the soft segment for latent heat storage, while aromatic diboronic acids including 1,4-phenyleneboronic acid (PBA) and 4,4′-biphenyldiboronic acid (BPBA) worked as cross-linkers within the hard segments. The incorporation of reversible boron-urethane bonds, together with hydrogen bonding, afforded covalently cross-linked networks, denoted as PEG6K-HDI-X, which exhibited an excellent combination of mechanical properties, solvent resistance, and thermally induced shape memory. PEG6K-HDI-BPBA exhibited a high tensile strength of ∼25.91 MPa, a fracture strain of ∼1502.71%, and a toughness of ∼278.44 MJ/m3, while maintaining an excellent thermal storage capacity of ∼94.3 J/g. The synergy of high mechanical strength, shape adaptability, excellent thermal storage capacity, and environmental durability rendered PEG6K-HDI-X highly suitable for advanced applications, particularly in wearable thermal therapy devices.