The polymer electrolytes composed of poly(acrylonitrile-co-methyl methacrylate-co-lithium methacrylate) [P(AN-co-MMA-co-LiMA)], ethylene carbonate (EC), LiClO4 salts, and silica have been prepared. The introduction of the MMA unit into the P(AN-co-LiMA) matrix made the polymer matrix soluble in a rather volatile solvent such as tetrahydrofuran (THF), which is expected to enhance the process for preparing the polymer electrolyte, The ion groups in the P(AN-co-MMA-coLiMA) were found to prevent EC from crystalling through their ion-dipole interactions with the polar groups in the EC. This suppression of the EC crystallization could lead to the enhancement of the ion conductivity at subambient temperature. Copyright (C) 2000 John Wiley & Sons, Ltd.