Monomers polypyrrole electrochemical conditions

Polypyrrole and many of its derivatives can be synthesized via simple chemical or electrochemical methods [120]. Photochemically initiated and enzyme-catalyzed polymerization routes have also been described but less developed. Different synthesis routes produce polypyrrole with different forms chemical oxidations generally produce powders, while electrochemical synthesis leads to films deposited on the working electrode and enzymatic polymerization gives aqueous dispersions [Liu. Y. C, 2002, Tadros. T. H, 2005 and Wallace. G. G, 2003]. As mentioned above the electrochemical polymerization method is utilized extensively for production of electro active/conductive films. The film properties can be easily controlled by simply varying the electrolysis conditions such as electrode potential, current density, solvent, and electrolyte. It also enables control of thickness of the polymers. Electrochemical synthesis of polymers is a complex process and various factors such as the nature and concentration of monomer/electrolyte, cell conditions, the solvent, electrode, applied potential and temperature, pH affects the yield and the quality of the film... 

About 10 years ago, deBerry [68] found that a reduction in the corrosion rate could be delivered by electrochemical coating of prepassivated steel (in passivating enviromnent) with polyaniline (from aniline monomer). He supposed that the preformed passive state of the metal was maintained by the PAni layer. Troch-Nagels et al. [69], however, concluded that PAni, unlike polypyrrole, after electrochemical deposition under comparable conditions, did not offer any corrosion protection. 

Polypyrrole can be synthesized by the galvanostatic or potentiostatic electrolysis of nonaqueous or aqueous solution containing pyrrole monomer and supporting electrolyte. Metals, such as Pt and Au, carbon, or semiconductors can be used as electrode materials. Pt is most often used for electrochemical measurements of polypyrrole film electrodes. The physical and electrochemical properties of synthesized polypyrrole are greatly influenced by the electrolysis current, potential conditions, electrode materials, concentrations of the pyrrole monomer and supporting electrolyte, electrolyte (dopant) and solvent materials, temperature, and so on. 

Polypyrrole can be deposited in either potentiostatic or galvanostatic conditions and by potential or current sweeps or pulses. In any case, the applied electrical conditions introduce effects on both structure and properties of the polymer. From electrochemical preliminary studies of the electrode in the absence and presence of the monomer (Fig. 1), we can choose the potential window in which monomeric oxidation will take place. When polymerization is initiated, side chemical polym-... 

The second problem associated with electrochemical synthesis of polypyrroles seems to be related to die difficulties found in correlating the polymer s properties with the conditions of synthesis. This has been derived from the widely spread idea of an overall understanding of the electrochemical mechanism. However, even the most simple electrochemical process of pyrrole electropolymerization involves different experimental variables in order to optimize polymer properties. These variables can be chemical, such as solvent or reactants (monomer and dopant salt), or physical, such as temperature, nature and shape of die electrodes, cell geometry or electrical conditions during synthesis. In addition, commonly the effects of all these variables are interdependent. 

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