Novel Polymer Electrolytes Based on Mono- and Bis-Oxetane Monomers with Oligo(Ethylene Oxide) Units

Abstract

New types of polymer electrolytes were prepared by cationic ring-opening copolymerization of bis-oxetane (R-O-(CH2CH2O)m-R, R = 3-ethyl-3-methylene oxetane unit, DDOE (m = 2), TrDOE (m = 3), TeDOE (m = 4)) and mono-oxetane (R-O-(CH2CH2O)n-CH3, TrMOE (n = 3), NoMOE (n = 9), DoMOE (n = 12)) with lithium salts as a catalyst, and were characterized by differential scanning calorimetry (DSC) and alternating impedance spectroscopy. The poly(oxetane)-based electrolytes had cross-linked networks with oligo(ethylene oxide) and 2-ethyltrimethylene oxide main chains and methoxyoligo(ethylene oxide) side chains. The polymer electrolytes prepared with LiBF4 revealed high conductivity, compared to those done with LiPF6 or LiN(C2F5SO2)2. The conductivities of the poly(oxetane)-LiBF4 complexes depended on the mono-oxetane content and the length of oligo(ethylene oxide) in the mono- and bis-oxetanes. The oligo(ethylene oxide) side chains in the complexes acted as efficient plasticizing agents, particularly using NoMOE or DoMOE. Maximum conductivities of the polymer electrolytes with LiBF4([Li]/[O] = 0.045) revealed 9.1 × 10−6 (TrMOE/DDOE mole ratio = 3.0) and 1.0 × 10−4 S cm−1 (NoMOE/DDOE = 1.72 and DoMOE/DDOE = 1.29).