Polyethylene glycol (PEG) and diacetate cellulose (CDA) exhibit good miscibility in acetone solution. The miscibility is related to the molecular weight of PEG, which increases as miscibility decreases. The phase-change behavior of PEG in composite with CDA prepared from the miscible solution was found to be completely different from that of pure PEG. When the PEG fraction in the composites was less than 85%, PEG within the composite did not melt into liquid; even when the temperature was 40degreesC higher than the melting point of PEG, the PEG-CDA composite exhibited solid-solid phase-change behavior. Thermal analysis indicated that the PEG-CDA composite had greater enthalpy and exhibited good thermal stability. The PEG-CDA composite that exhibited solid-solid phase-change behavior can be used as a new kind of phase-change material for thermal energy storage and temperature control. (C) 2003 Wiley Periodicals, Inc.