Poly(3-methylthiophene) oxidation under chemical control. Rate coefficients change with prepolarization potentials of reduction

A kinetic study based on the potentiostatic oxidation of poly(3-methylthiophene) is presented. The influence of different initial states obtained by the reduction of the film at rising cathodic potentials for the same prepolarization time was studied. At the chronoamperometric maxima, the oxidation occurs under chemical control as shown by the semilogarithmic relationships between current and chemical concentrations. The oxidation rate coefficient changes as a function of both the oxidation overpotential, as for any other electrochemical oxidation, and the reduction potential of prepolarization. This dependence on the cathodic prepolarization shows two ranges: constant rate coefficients were obtained after reduction by prepolarization at low cathodic potentials and an exponential decrease of the rate coefficient after reduction at increasing cathodic prepolarizations. The conformational relaxation model allows a good description and quantification of these results.