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).