Electrochemical polymerization of 3-alkylthiophenes was performed in the presence of a small amount of 2,2′-bipyrrole, indole, 5-methoxyindole, 2,2′-bithiophene, or 2,2′:5′,2″-terthiophene. The presence of these additives effects a significant increase in the rate of polymerization. The applied potentials required for the polymerization to proceed can be reduced to values lower than the oxidation potentials of the monomers. The reaction rate was found to be first order in the monomer concentration and 0.5 order in the additive concentration. The first-order dependence of the rate in monomer concentration was also observed in the polymerization with 2,2′-bithiophene or 2,2′:5′,2″-terthiophene as the monomer. The activation energies for the polymerization of 3-methylthiophene were measured both in the absence and in the presence of 2,2′-bithiophene or 2,2′:5′,2″-terthiophene. The presence of the additives results in a decrease in the activation energy and an increase in the preexponential factor. The activation enthalpies, activation entropies, and Gibbs free energies of activation were also evaluated. All the results are interpreted based on the mechanism that the polymer chain growth is accomplished by electrophilic aromatic substitution reaction of radical cation intermediates with neutral monomers.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry