Preparation and properties of β-cyclodextrin/4,4′-diphenylmethane diisocyanate/polyethylene glycol (β-CD/MDI/PEG) crosslinking copolymers as polymeric solid–solid phase change materials

• Four crosslinking β-CD/MDI/PEG copolymers were synthesized as solid–solid PCMs.
• The copolymers have spherocrystal morphology with smaller size than that of PEG.
• The crosslinking density of the copolymers effects their phase change properties.
• The copolymers have high phase change enthalpy and good thermal reliability.

Four β-cyclodextrin/4,4′-diphenylmethane diisocyanate/polyethylene glycol (β-CD/MDI/PEG) crosslinking copolymers with different crosslinking density were prepared and characterized as novel polymeric solid–solid phase change materials (SSPCMs) for thermal energy storage. In the SSPCMs, PEG acts as the phase change functional chain and β-cyclodextrin (β-CD) acts as the molecular framework. The results from wide-angle X-ray diffraction (WAXD) and polarizing optical microscopy (POM) show that the synthesized SSPCMs have good crystallization properties and spherocrystal morphology with smaller size than that of PEG. According to the results of differential scanning calorimetry (DSC) and thermogravimetry (TG) curves, the SSPCMs possess high phase change enthalpies, good reusability, thermal reliability and stability. It is concluded that the crosslinking density of SSPCMs is a crucial factor significantly influenced the free movement and crystallization of PEG segments, and then affects phase transition properties of SSPCMs.