The copolymer ethylene oxide and epichloridrine doped with lithium perchlorate shows interesting properties as an ionic conducting polymer mainly because of its amorphous structure at room temperature and its low glass transition temperature (T-g = -40 degrees C). C-13, Li-7 and H-1 nuclear magnetic resonance studies were performed in order to analyze the interactions between the polymer matrix and the dopant salt with solvent molecules. These studies and conductivity measurements were used to investigate the influence of the preparation method and the properties of the solvent on the physicochemical characteristics of the polymer electrolyte. Experimental results show that solvent molecules are retained in the solid polymer electrolyte, strongly modifying its ion transport dynamic, This fact can be related to the increase in the ionic conductivity when solvent molecules rest inside the polymer matrix, producing a plasticizing effect.