A series of aliphatic polyetheresters of poly(ethylene glycol) and diacyl chloride containing a different number of methylene units was synthesized, The polyetheresters synthesized were complexed with lithium perchlorate to obtain a polymer electrolyte with high ionic conductivity and reduced crystallinity. The effect of polymer structure on the ionic conductivity and thermal properties of the polymer electrolytes was investigated. The ionic conductivity behavior of these samples was analyzed in terms of their thermal properties, Li-7 NMR spin-spin relaxation studies were also carried out in order to investigate the local environments and dynamics of ions in the polymer electrolytes.