ELECTROCHEMICALLY INITIATED CHAIN POLYMERIZATION OF PYRROLE IN AQUEOUS-MEDIA

The electrochemical quartz crystal microbalance has been employed to investigate the electropolymerization of pyrrole in a variety of aqueous electrolytes. In contrast to the generally accepted cation-radical coupling process for the electropolymerization of pyrrole, an electrochemically initiated chain polymerization, featuring a high polymerization rate and involving little charge transport, was found under specific conditions in the presence of ClO4-, BF4- and PF6- electrolytes. The more typical cation-radical coupling mechanism, characterized by a constant polymerization charge to mass deposited ratio, is observed in the presence of Cl-, NO3-, dodecyl sulfate, copper phthalocyanine tetrasulfonate, beta-cyclodextrin tetradecasulfate, and poly(styrene sulfonate). Electrochemical characterizations of polypyrrole films prepared in aqueous ClO4- electrolytes reveal that the polymer formed via chain polymerization exhibits the ability to transport both cations and anions during electrochemical switching between redox states, while the polymer synthesized through cation-radical coupling is only capable of transporting a single ionic species.