Abstract: The present invention provides a process for the preparation of ion-exchange membranes for use in electromembrane processes. The membranes are prepared from a solution, in a dipolar-aprotic solvent, containing (a) a polymeric sulfonic acid or a polymeric sulfonate salt of formula Polymer-SO3X, where X is H or a monovalent cation, and (b) a basic polymer containing primary, secondary or tertiary basic N. The dissolved polymer blend is spread in a thin layer onto a support, and the solvent is evaporated to form a polymeric film. The films produced by the process are particularly useful as ion-exchange membranes due to improved properties relative to the component polymers with regard to ionic conductivity, swelling permselectivity, and thermal resistance.