Recent developments in polymer electrolytes have focused on preparation of composites using nano/micron size ceramic particles such as SiO2, TiO2, Al2O3, BaTiO3, and MgO. We reporthere the preparation and characterization of an all-solid state polyethylene oxide (PEO) composite electrolyte from PEO(375)-SiO2, high molecular weight PEO (MW=600 K) and LiClO4 (O/Li= 16/1). Oligomeric PEOs, with ethylene oxide (EO) repeat units 6-9 (< MW >=375 g/mol), were chemically grafted (similar to 30 wt.%) to fumed silica (A380) using a trimethoxy PEO(375)-silane. The surface grafted PEO chains were disordered (no crystallization) and less mobile than the free chains, with the glass transition temperature (T-g) increasing from -90 degrees C [PEO(375)-silane] to -54 degrees C [PEO(375)-SiO2]; addition of LiClO4 (O/Li=8/1) further raised T-g to -34 degrees C. Nanocomposite electrolytes with good dimensional stability were obtained by blending 14-wt.% PEO(375)-SiO2 with semicrystalline PEO(600 K)/LiClO4 (O/Li = 16/1). Conductivities (g) were 10 to 4 times greater [between 10 degrees C(sigma=2.1 x 10(-8) S/cm) and 40 degrees C(sigma= 1.1 x 10(-5) S/cm), respectively] than for neat PEO(600 K)or for composite electrolytes having the same amount of native fumed silica, SiO2. No conductivity improvements were observed above T-m or for amorphous PEO (600 K)/LiClO4 (O/Li=8/1) with addition of SiO2 or PEO(375)-SiO2. (C) 2008 Published by Elsevier B.V.