Phase change material with flexible crosslinking for thermal energy storage

The utilization of renewable energy through phase change materials (PCMs) is particularly attractive for the realization of sustainable society. Herein, a flexible but reliable solid–solid PCM was successfully synthesized by the integration of quadruple H‐bonding crosslinks with polyethylene glycol (PEG)‐based polyurethanes. The strong quadruple H‐bonding from the dimerization of 2‐ureido‐4 [1H]‐pyrimidinone (UPy) units could act as dynamic cross‐links to maintain shape stability. PEG chains in flexible polymer network serve as phase change ingredients, affording thermal energy storage capacity. The physical crosslink density and phase change enthalpy can be adjusted. In contrast to chemical crosslinks, the physical crosslinks of UPy provide reprocessability of the prepared PCMs and show little hindrance on the crystallization of PEG chains. The chemical structure, phase transformation, crystallization, and thermal properties of prepared PCMs were characterized by fourier transform infrared spectroscopy, differential scanning calorimetry (DSC), X‐ray diffraction, polarizing microscope, and thermogravimetric analysis. DSC analysis shows that the prepared PCM can store 101.9 J g−1 when PCMs undergo phase change process. Moreover, the accelerated thermal cycling test and leakage test are also conducted to illustrate the thermal reliability and shape‐stable properties. These PCMs that possess high phase change enthalpy and outstanding reprocessability are alternative for solar energy collection and waste heat recovery.