Polymer electrolytes derived from polynorbornenes with pendent cyclophosphazenes: poly(ethylene glycol) methyl ether (PEGME) derivatives

A novel elastomeric polymer electrolyte was developed by the linkage of pol y(ethylene glycol) methyl ether (PEGME) side chains and norbornene-based un its to a cydotriphosphazene ring, followed by polymerization of the norborn ene units by ring-opening metathesis polymerization (ROMP). This yielded an organic polymer backbone with ion co-ordinative cyclic phosphazene side gr oups. Adjustment of the norbornene content in the starting monomer allowed the degree of branching and cross-linking to be controlled and, in turn, th e mechanical properties of the material to be tuned. The polymers were comp lexed with fixed molal ratios of LiN(SO2CF3)(2) and LiSO3CF3 and examined a s solid polymer electrolytes. Polymer gel electrolytes were then formulated by the addition of variable amounts of propylene carbonate to the polynorb ornenes. Films of solvent-free and solvent-containing polymers were homogen eous, flexible and self-standing materials. The ionic conductivities of the solvent-free polymers were in the range of 4 x 10(-5) Slcm at 30 degreesC in the presence of 40 mol% of LiSO3CF3 or LiN(SO2CF3)(2). The conductivitie s of the solvent-containing (gel) systems increased with increases in the p ropylene carbonate content to a value of 2 X 10(-3) S/cm at 30 degreesC in the presence of 50 wt.% of propylene carbonate and with the use of LiN(SO2C F3)(2) at a constant O:Li+ ratio of 8:1. Even with this high concentration of propylene carbonate, the electrolyte was a solid elastomer rather than a viscous liquid. In general, the conductivities are twice as high with the use of LiN(SO2CF3)(2) compared to LiSO3CF3. The T-g values were determined by DSC analysis, and these decreased with increased amounts of propylene ca rbonate in the system. (C) 2001 Elsevier Science B.V. All rights reserved.