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Abstract

Electronically conducting polymer films were prepared electrochemically from aqueous electrolytes containing mixtures of pyrrole and N‐(3‐sulfopropyl)pyrrole. The reversible electrochemical oxidation and reduction (redox‐switching) of these coatings have been studied, mainly with the method of cyclic voltammetry. At various electrode potentials the coated electrodes were withdrawn from the solutions to determine the composition of the films gravimetrically and by energy‐dispersive analysis of X‐rays (EDAX). Volta‐potential measurements were conducted to obtain information on the Donnan‐potentials. Thus the membrane properties of the coatings were characterized as a function of the electrode potential and the mole fraction of sulfonate groups fixed in the copolymer matrix. While conventional polypyrrole films constitute anion exchangers in the oxidized state, the copolymers can be either anion‐ or cation‐exchangers, depending on the concentration of the fixed anions. When the polymer matrix contains about one sulfonate group per 10 pyrrole units, the film undergoes, during redox‐switching, a reversible and complete transition between anion‐ and cation‐exchange character.