Thermal Energy Storage Using Poly(ethylene glycol) Incorporated Hyperbranched Polyurethane as Solid-Solid Phase Change Material

For efficient energy storage, hyperbranched (HB) architecture was adopted to prepare a series of HB polyurethanes via A₂ + B₃ approach with isocyanate terminated poly(ethylene glycol) (PEG) as branching unit and phloroglucinol (PG) as aromatic core. The chemical structure of the HB polymer was confirmed using FTIR and NMR. The gel permeation chromatography and solution viscosities indicate polymers of moderately high molecular weights. The thermal behavior and crystalline properties were investigated using differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction, and polarized optical microscopy. A high fusion enthalpy of 146.6 J g^-1 at transition temperature of 56 °C was achieved. Thermal stability was found to be quite high (up to 300 °C), and thermal reliability was retained with no chemical degradation after thermal cycling. The polymer exhibited crystalline to amorphous phase change above the transition temperatures and back, which makes it attractive as a polymeric phase change material for thermal energy storage applications.