A novel cyclic ether monomer 3-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxymethyl}-3'-methyloxetane (HEMO) was prepared from the reaction of 3-hydroxymethyl-3'-methyloxetane tosylate with triethylene glycol. The corresponding hyperbranched polyether (PHEMO) was synthesized using BF3 (.) Et2O as initiator through cationic ring-opening polymerization. The evidence from H-1 and C-13 NMR analyses revealed that the hyperbranched structure is constructed by the competition between two chain propagation mechanisms, i.e. active chain end and activated monomer mechanism. The terminal structure of PHEMO with a cyclic fragment was definitely detected by MALDI-TOF measurement. A DSC test implied that the resulting polyether has excellent segment motion performance potentially beneficial for the ion transport of polymer electrolytes. Moreover, a TGA assay showed that this hyperbranched polymer possesses high thermostability as compared to its liquid counterpart. The ion conductivity was measured to reach 5.6 x 10(-5) S/cm at room temperature and 6.3 x 10(-4) S/cm at 80 degrees C after doped with LiTFSI at a ratio of Li:O = 0.05, presenting the promise to meet the practical requirement of lithium ion batteries for polymer electrolytes. (c) 2006 Wiley Periodicals, Inc.