CORROSION OF CONDUCTING POLYMERS IN AQUEOUS-ELECTROLYTES

The corrosion of polythlophene, poly-bisthiophene and poly-3-methylthi ophene in aqueous electrolytes at pH 1 to 13 was investigated. Corrosi on rate was determined experimentally by potentiodynamic discharge of residual redox capacity of the conducting polymer after exposure to th e corrosion medium. Two corrosion reactions were found to proceed afte r quasi first order kinetics. The initial rapid process is due to an e lectrochemical mechanism. The cathodic undoping is balanced by an anod ic overoxidation reaction, even at the relatively negative potentials. A rather slow second process is caused by chemical attack of nucleoph iles dissolved in the solid at the remaining radical cationic centers. Both rate constants are appreciably larger than those measured previo usly for polypyrrole. and they increase with increasing pH. The accele ration is due to the more positive redox potentials for the polythioph enes. From the exponential decay of the corrosion potential with time, the same rate constants could be evaluated. In contrast to polypyrrol e, the polymer backbone conjugation is not interrupted initially due t o -S- --> SO2-, and recharge is possible to some extent.