Poly[oxymethylene‐oligo(oxyethylene)]s with uniform oxyethylene sequence lengths, 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 were noncrystalline at room temperature, whereas a polymer‐salt complex ( , 50°C) formed in the mixtures with the polymer with . Glass transition temperatures increased as salt concentration increased with a linear dependence of on . Maximum conductivities at room temperature were found at salt concentrations in the range 0.7–1.0 mol kg−1 : e.g., for the polymer with . The maximum conductivities were invariably smaller than those found for a comparable polymer prepared from polyethylene glycol 400, i.e., with and a narrow distribution of chain lengths.