Novel ion-exchange membranes composed of dimethyl 5-sulfoisophthalate sodium salt (DMSIP), 1,6-hexanediol (HDO), isophthalic acid (IPA) and maleic anhydride (MA) were prepared by the synthesis of a DHIM oligomer and UV-cross-linking. The basic properties of the membranes were characterized, and a redox flow battery (RFB) test was conducted. The conversion and molecular weight of the DHIM oligomer decreased with increasing DMSIP contents; the maximum conversion and molecular weight values were 90.8% and 1335-1620 g/mol, respectively. The thermal stability of the cross-linked DHIM ion-exchange membrane was 370 degrees C. The water uptake and ion-exchange capacity increased as the DMSIP contents increased, and the maximum values were 43.1% and 1.23 meq/g. The minimum values for the electrical resistance and ion transport were 0.27 Omega cm(2) and 0.998, respectively. Charge-discharge, voltage and energy efficiencies increased with the increasing extent of cross-linking, and their values were 90.81%, 79.92% and 71.52%, respectively. The minimum value of methanol permeability was lower than that of Nafion 117 (R), which indicates that the membrane has higher ion selectivity than Nafion 117 (R). (C) 2013 Published by Elsevier B.V.