A series of poly(aryl ether sulfone) copolymers containing quaternary ammonium moieties were obtained by polymerization of methylated copolymers, followed by bromination and derivatization with quaternary-ammonium groups. The copolymer membranes exhibited excellent thermal stability and mechanical properties. Symmetric supercapacitor single cells based on activated carbon and quaternary ammonium functionalized poly(aryl ether sullone) membranes were fabricated into a three-layer structure: activated carbon electrode//quaternary ammonium functionalized poly(aryl ether sulfone) separator//activated carbon electrode and characterized by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy in 6 M KOH aqueous solution. The coulombic efficiency of the supercapacitor was as high as 95% over 5000 cycles. The effect of different degree of quaternization of PAES copolymer separators on thermal and mechanical properties of separators and performance of the symmetric supercapacitor single cells were investigated. (C) 2014 Elsevier B.V. All rights reserved.