Low crosslinked copolymer of linear and hyperbranched polyurethane (CHPU) was prepared, and the ionic conductivities and thermal properties of the composite polymer electrolytes composed of CHPU and LiClO4 were investigated. The FTIR and Raman spectra analysis indicated that the polyurethane copolymer could dissolve more lithium salt than the corresponding polymer electrolytes of the non crosslinked hyperbranched polyurethane, and showed higher conductivities. At salt concentration EO/Li = 4, the electrolyte CHPU30-LiClO4 reached its maximum conductivity, 1.51 X 10(-5) S cm(-1) at 25 degrees C. DSC measurement was also used for the analysis of the thermal properties of polymer electrolytes. (c) 2007 Wiley Periodicals, Inc.