The oxidation of poly(3-methylthiophene) films in acetonitrile solutions was studied by anodic potential steps using as initial states films reduced by cathodic prepolarizations during different reduction times. A kinetic study was performed for different prepolarization times changing every time one of the experimental variables: the electrolyte concentration, or the anodic potential of oxidation. Double logarithmic dependencies of the current at the chronoamperometic maxima with the reactant concentrations corroborate the chemical kinetic control of the oxidation around that maximum. The experimental oxidation rate coefficient is a function of either the cathodic potential of prepolarization or the prepolarization time. Whatever the cathodic potential of prepolarization, the rate coefficient decreases at rising prepolarization times. The attained results can be theoretically described by the conformational relaxation model. The inclusion of the polarization time in the relaxation model allows defining a new magnitude: the molar energy of conformational packing per degree of temperature and per second of prepolarization, gamma, an empirical constant obtained by Netchtschein 15 years ago. All the studied films present two gamma: indicating that two different structures, having two packing conformational energies per K and per second, constitute the material. (c) 2008 Elsevier B.V. All rights reserved.