Polynorbornenes bearing pendent cyclotriphosphazenes with oligoethyleneoxy side groups: Behavior as solid polymer electrolytes

Three different polynorbornenes (PNB) with pendent cyclotriphosphazene side units that bear different short-chain oligoethyleneoxy side groups were synthesized via ring-opening metathesis polymerization (ROMP). Polymers with methoxyethoxy (-OCH₂CH₂)_nOCH₃ (n = 1), di(ethylene glycol) methyl ether (n = 2), and tri(ethylene glycol) methyl ether (n = 3) were synthesized and characterized by multinuclear NMR, GPC, DSC, and elemental analysis. The solid polymers were complexed with LiSO₃- CF₃ and LiN(SO₂CF₃)₂ (10-60% molar ratios), and the ionic conductivities were measured by impedance analysis as a function of temperature. The polymers with methoxyethoxy side units showed no detectable ambient temperature conductivities within the limitations of the impedance analyzer. The conductivities of the other polymer electrolytes increased as the concentration of salt was increased, with similar maximum conductivities found for the di(ethylene glycol) and tri(ethylene glycol) systems (2.1×10^-5 S/cm at 30 °C with the use of 40 mol% LiN(SO₂CF₃)₂ in both cases). The conductivities showed non-Arrhenius temperature dependence. No melting or crystallization transitions were detected at temperatures above 25 °C for any of polymer-salt complexes tested. Modification of one polymer with -O(CH₂CH₂O)₃CH₃ side chains was carried out by epoxidation of the backbone C = C bonds.