Two novel polyethers, one comb-like and another hyperbranched, were synthesized by the cationic ring-opening polymerization of 3-(methoxy(triethylenoxy)) methyl- and 3-(hydroxy-(triethylenoxy))methyl-3'-methyloxetane, respectively. The former reacted with a multifunctional isocyanate and the latter with a difunctional isocyanate to give rise to the corresponding crosslinked poly(ether urethane) elastomers, PCEU and PHEU. Accordingly, two kinds of solid polymer electrolytes (SPEs) were prepared from these two elastomers in situ in the presence of lithium salt trifluoromethanesulfonimide. It was found that the PCEU-based SPEs shows a higher ionic conductivity than that PHEU-based ones due to its more mobile pendent chains and appropriate crosslinking density in the polymeric network. The maximum ionic conductivities of 1.4 x 10(-5) S/cm at 30 degrees C and 3.5 x 10(-4) S/cm at 80 degrees C were attained at the molar ratio of O/Li = 7.5. The DSC measurements clearly demonstrated that PCEU indeed possesses the more flexible chain motion ability than PHEU. The electrochemical stability window of PCEU, which is 1.7-4.0 V was measured by cyclic voltammogram. Additionally, the significantly high decomposition temperature as evidenced by TGA analyses endowed these SPEs a good safe performance. (C) 2008 Wiley Periodicals, Inc.