Polymeric electrolytes obtained by the free radical polymerization of methyl methacrylate in a solution of LiCF3SO3 in an ethylene oxide-propylene oxide copolymer are studied. These electrolytes exhibit ambient temperature conductivities up to 3 x 10(-5) S/cm. Impedance spectroscopy experiments performed in a symmetrical cell with two lithium electrodes show that the properties of lithium electrode-polymer electrolyte interface are improved after the in situ polymerization of methyl methacrylate in the electrolyte. The growth of the resistance of the passive layer formed on the electrode-electrolyte interface is suppressed. The impedance studies are coupled with FT-IR measurements which show that the fraction of contact-ion pairs is reduced in electrolytes for which limited growth of the resistance of the passive layers is observed.