Effect of oxyethylene sequence length on the properties of poly(oxymethylene-oligo(oxyethylene))/LiClO sub(4) polymer electrolytes

Poly(oxymethylene-oligo(oxyethylene))s with uniform oxyethylene sequence lengths, m = 3-6 were prepared by oxymethylene-linking triethylene glycol to hexaethylene glycol. The thermal and electrochemical properties of mixtures of the polymers with lithium perchlorate were determined. The polymer-salt mixtures prepared from polymers with m = 4-6 were noncrystalline at room temperature, whereas a polymer-salt complex (T sub(m) approximately 323 K, 50 degree C) formed in the mixtures with the polymer with m = 3M. Glass transition temperatures increased as salt concentration increased with a linear dependence of 1/T sub(g) on c. Maximum conductivities at room temperature were found at salt concentrations in the range 0.7-1.0 mol kg super(1) (O/Li = 20-30); e.g., 3 x 10 super(-5) S cm super(-1) for the polymer with m = 5. The maximum conductivities were invariably smaller than those found for a comparable polymer prepared from polyethylene glycol 400, i.e., with m = 9 and a narrow distribution of chain lengths.