Abstract: Using polyethylene glycol (PEG) as soft segments，1，4-butanediol(BDO)as chain extender, and modified MDI as curing agent，a series of polyurethane phase change materials (PUPCM) was obtained. The change in morphology and properties of PUPCM during heating-cooling cycles was online observed using polarization microscope(POM)，differential scanning caborimetry(DSC)，and other testing methods. Atomic force microscope(AFM) revealed that the nature of phase change during the thermal cycling was the crystalline-amorphous transition and the resulted microphase separation，which influenced the thermodynamic and crystallization properties.

Key words: PUPCM, microphase separation, phase change substance