Synthesis and optical, electrical, and thermoelectric properties of sodium salts of polyaniline sulfonic acid

Sodium salts of poly(aniline-5-sulfonic acid) (PAS), The PAS(Na)s, were obtained by the reaction of PAS with NaOH in water. The degree of sodium sulfonation of the PAS(Na)s depended on the feed amount of NaOH. The absorption peak of the PAS(Na)s, corresponding to an exciton transition generated by self-doping in the polymer backbone, decreased with the number of sodium sulfonated units. The PAS(Na)s were subjected to electrochemical oxidation, and the two oxidation peaks shifted to a lower potential as the degree of sodium sulfonation increased. The electrochemical reaction was accompanied by electrochromism. Thermoelectric measurements of the PAS(Na)s suggested that the majority of carriers were holes. The Seebeck coefficients (S′s) of the PAS(Na)s increased as the degree of sodium sulfonation of the polymers increased.