Proton-conducting polymer electrolytes based on methacrylates were prepared by direct, radical polymerization of ethyl (EMA), 2-ethoxyethyl (EOEMA), and 2-hydroxyethyl methacrylate (HEMA). Samples with embedded solutions of phosphoric acid in propylene carbonate (PC), gamma-butyrolactone (GBL). N,N-dimethylformamide (DMF) and their mixtures were studied using impedance, voltammetrical and thermogravimetric methods. Membranes of long-term stability exhibit ionic conductivity up to 6.7 x 10(-5) S cm(-1) at 25 degrees C reached for the sample PEMA-PC-H3PO4 (31:42:27 mol.%). The accessible electrochemical potential window is 2.2-3V depending on the working electrode material (glassy carbon or platinum). The thermogravimetric analysis shows that the membranes are thermally stable up to 110-130 degrees C. (C) 2008 Elsevier Ltd. All rights reserved.