Synthesis and application as polymer electrolyte of hyperbranched copolyethers derived from cationic ring-opening polymerization of 3-{2-[2-(2-methoxyethoxy)ethoxy]ethoxy}methyl- and 3-hydroxymethyl-3′-methyloxetane

A kind of novel hyperbranched copolyethers intending for the solid polymer electrolyte was synthesized via the cationic ring-opening polymerization of 3-{2-[2-(2-methoxyethoxy)ethoxy]-ethoxy}methyl-3′-methyloxetane (MEMO) and 3-hydroxymethyl-3′-methyloxetane (HMO) in the presence of BF₃·Et₂O as an initiator. Herein HMO was employed to create the hyperbranched structure, whereas MEMO was responsible for the ionic transportation of the resulting copolymers. The terminal structure featured by a cyclic fragment was definitely detected by MALDI-TOF measurement. The degree of branching of the copolymers was calculated by means of ¹³C NMR spectra. The DSC analysis implied that they hold the excellent segment motion performance and perfectly amorphous state beneficial for the ionic transportation. The ionic conductivity measurements showed that the sample HMO 30 reaches a maximum ionic conductivity of 8.0 × 10^-5 S/cm at 30 °C and 7.4 × 10^-4 S/cm at 80 °C, respectively, after doping with lithium salt LiTFSI. Moreover, the TGA assay exhibited that these hyperbranched copolymers possess the higher thermostability as compared with their liquid counterparts.