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Solid polymer electrolytes (SPEs) systems based on interpenetrating blends of poly(ethylene oxide-co-propylene oxide) and poly(methyl methacrylate) host matrices, with lithium perchlorate as guest salt, were prepared. These electrolytes were presented as free-standing films, and their thermal and electrochemical properties were characterized by conductivity and electrochemical stability measurements. The properties of the interpenetrating blends of poly(ethylene oxide-co-propylene oxide) and poly(methyl methacrylate) host matrices as the electrolyte component of a solid-state electrochromic device are reported and the results obtained suggest that this electrolyte provides an encouraging performance in this application. The most conducting electrolyte composition of this SPE system is the formulation designated as SPE2-0PC (5.01x10-4 S cm-1 at about 57ºC). The lowest decomposition temperature was registered with the SPE6-15PC composition (233ºC). The average transmittance in the visible region of the spectrum was above 41 % for all the samples analyzed. After coloration the device assembled with 71 wt % PC presented an average transmittance of 15.71 % and an optical density at 550nm of 0.61