A series of aliphatic polyesters of sebacoyl chloride and poly(ethylene glycol) containing a different number of ethylene oxide groups was synthesized and characterized. These polyesters were complexed with lithium perchlorate to obtain a new class of polymer electrolyte. The relationships between the structure and properties of these polymer electrolytes were investigated. The main factor that affects the ionic conductivity in these systems was found to be the solvating capacity of the polyester for the lithium salt. These polymer electrolytes showed ionic conductivities up to 10(-5) similar to 10(-4) S/cm at 25 degrees C. The mechanical strength was improved by cross-linking, and the cross-linked polyester complexed with a LiClO4 salt showed an ionic conductivity of 2 X 10(-5) S/cm at room temperature. Li-7 NMR spin-spin relaxation and dielectric relaxation studies were also carried out to investigate the local environments and dynamics of ions in the polymer electrolytes.