Solid–solid phase-change materials based on hyperbranched polyurethane for thermal energy storage

A hyperbranched polyol (HBP) was synthesized with poly(ethylene glycol) (PEG) as the core molecule and 2,2-bis(hydroxymethyl) propionic acid as the chain extender. Then, a series of hyperbranched polyurethane phase-change materials (HP-PCMs) with different crosslinking densities was synthesized with isophorone diisocyanate and HBP as a molecular skeleton and PEG 6000 as a phase-change ingredient. 1 H-NMR, gel permeation chromatography, and Fourier transform infrared spectroscopy confirmed the successful synthesis of the HBP and HP-PCMs. The polarization optical microscopy and wide-angle X-ray diffraction results show that the HP-PCM exhibited good crystallization properties, but the crystallinity was lower than that of PEG 6000. The analysis results from differential scanning calorimetry indicated that the HP-PCMs were typical solid–solid phase-change materials with suitable phase-transition temperatures. In addition, HP-PCM-3, with an appropriate degree of hyperbranched structure, possessed the highest thermal transition enthalpy of 123.5 J/g. Moreover, thermal cycling testing and thermogravimetric analysis showed that the HP-PCMs exhibited good thermal reliability and stability. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45014.