Breaking the Trade-Off of Mechanical Robustness and Energy Storage Capacity in Phase Change Materials Through a...

Phase change materials (PCMs) have garnered significant attention for personal thermal management, yet conventional solid-liquid PCMs suffer from potential leakage issues, and existing solid-solid polyurethane-based PCMs (PU-PCMs) often face an inherent trade-off between mechanical robustness and energy storage capacity. Here, we develop a molecular design strategy of hard-segment-anchored/side-chain-storage to decouple these competing functions by relocating the phase-change units from the polymer main chain to side chains. Specifically, a series of flexible side-chain PU-PCMs were synthesized using 2,2'-(octadecylimino)diethanol (SDEA) bearing crystallizable C18 alkyl side chains and 1,4-butanediol (BDO) as chain extender. The hard segments formed by BDO and hexamethylene diisocyanate provide a robust physical network, while the hanging C18 side chains independently crystallize to enable solid-solid phase transition and latent heat storage. By adjusting the BDO-to-SDEA molar ratio, the optimized material, SPU-BDO_0.20, exhibits a desirable combination of high toughness, excellent flexibility (elongation at break >600%), high phase change enthalpy (51.1 J g^{- 1}), and outstanding thermal cycling stability (500 cycles). Notably, electrospun fibrous membranes fabricated from SPU-BDO_0.20 demonstrate effective temperature regulation, maintaining a surface temperature 3°C-4°C lower than cotton controls under heating. This work provides a new strategy for developing high-performance, flexible, and leakage-free PCMs for wearable thermal management applications.