Cellulose-graft-poly(ethylene glycol) copolymers were synthesized, and the thermal properties of the copolymers were investigated. The cellulose-graft-poly(ethylene glycol) copolymers showed solid-solid phase-transition behavior with a high thermal storage density and good thermal stability in the temperature region of 25-250 degrees C. The phase-transition temperature and enthalpy of the cellulose-graft-poly(ethylene glycol) copolymers could be adjusted through changes in the poly(ethylene glycol) content. The prepared copolymers could be used as thermal energy storage materials. (C) 2008 Wiley Periodicals, Inc.