Electrochemistry of conductive polymers XVI. Growth mechanism of polypyrrole studied by kinetic and spectroelectrochemical measurements

The growth mechanism of polypyrrole has been studied in acetonitrile by kinetic and spectroelectrochemical measurements. The results indicate that the polymerization reaction rate is 13 ∼ 12 order with respect to the pyrrole concentration and 13 order with respect to the amount of polypyrrole. In-Situ spectroelectrochemical studies at lower pyrrole concentrations indicate that reasonably high steady state concentrations of trimeric and tetrameric species are maintained during the polymerization reaction. From these observations, we conclude that: (1) both the monomer and polymer films are important for the growth (from the rate equation), (2) the formation of dimeric species appears to present the rate limiting step for the reaction (from the reaction order), (3) polymers grow in one-dimension, and (4) further growth of polymers from trimeric and tetrameric species requires a high monomer concentration.