Mechanisms polyaniline electrochemical polymerization

Scheme 12.2. Aniline to polyaniline electrochemical polymerization mechanism (adapted from reference [89]).

Completely different monomers were called for. Before long, three of today s workhorses had been identified pyrrole, aniline and thiophene. In Japan, Yamamoto [38] and in Germany, Kossmehl [39] synthesized polythiophene doped with pentafluoroarsenate. At the same time, the possibilities of electrochemical polymerization were recognized. At the IBM Lab in San Jose, Diaz used oxidative electrochemical polymerization to prepare polypyrrole [40] and polyaniline. [41] Electrochemical synthesis forms the polymer in its doped state, with the counter-ion (usually an anion) incorporated from the electrolyte. This mechanism permits the selection of a wider range of anions, including those which are not amenable to vapor-phase processes, such as perchlorate and tetra-fluoroborate. Electrochemical doping also overcomes an issue associated with dopants... 

Optical techniques have been used to clarify the electronic conduction mechanism and the electrochemical film conversion process [142-144]. Redondo et al. [143] employed ellipsometry [144] to optically probe films grown on platinum electrodes in hydrochloric acid solutions. The optical information may be used to draw conclusions on film density variations as a function of polymerization conditions and film thickness. More important, by potential cycling, films could be examined while undergoing conversions from the reduced (insulating) forms to the oxidized (conducting) forms. Redox reactions carried out on polyaniline-coated electrodes suggest that polyaniline conducts solely in its oxidized emeraldine salt state. 

Electronic and steric effects of substituents on polyaniline clearly influence the polymerization. These effects have been studied in the hope of obtaining a clearer understanding of the polymerization mechanism. A polymerization mechanism has been proposed from an investigation of the electrochemical oxidation of N-phenylaniline and /V-naphthylaniline in acetonitrile [166]. Films synthesized for this study underwent multiple color changes. The poly(N-naphthylaniline) films (a =... 

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