A series of comb-type amphiphilic copolymers (PES-g-PEO) with a stiff poly(aryl ether sulfone) backbone and flexible PEO side chains was synthesized via a "grafting onto" technique. By controlling the monomer feed ratios, high molecular weight copolymers with a range of PEO side chain content were prepared and used to form tough and flexible membranes. The PES-g-PEO membranes displayed high thermal stability (T(d) > 230 degrees C) and good mechanical properties. The water contact angles of the PES-g-PEO membranes ranged from 60.5 degrees to 66.7 degrees, 20 degrees lower than those of poly(aryl ether sulfone) membranes (82-86 degrees), indicating that the PEO side chains improved the hydrophilicity of the membranes. Wide-angle X-ray diffraction results indicated that the PES-g-PEO membranes possessed an amorphous structure, that is, crystallization of the PEO side chains did not occur. The Li-ion conductivity reached 2.26 x 10(-4) S/cm at room temperature, much higher than that of the pure PEO-based system (10(-6) S/cm), due to the presence of the amorphous PEO side chains between the PES backbones, which provided an effective Li-ion transport pathway. (C) 2011 Elsevier Ltd. All rights reserved.