Diaz, polypyrrole

In 1979, Diaz et al. produced the first flexible, stable polypyrrole (PPy) film with high conductivity (1(X) Scm ). The substance was polymerized on a Pt-electrode by anodic oxidation in acetonitrile. The then known chemical methods of synthesis " usually produced low conductivity powders from the monomers. By contrast, electropolymerization in organic solvents formed smooth and manageable films of good conductivity. Thus, this technique soon gained general currency, stimulating further electropolymerization experiments with other monomers. In 1982, Tourillon... 

Diaz AF, Logan JA(1980)Electroactive polyanihne films. JElectroanalChem 111 111-114 Noufi R, Nozik AJ, White J, Warren LF (1982) Enhanced stability of photoelectrodes with electrogenerated polyanUine films. J Electrochem Soc 129 2261-2265 Noufi R, Tench D, Warren LE (1981) Protection of semiconductor photoanodes with photoelectrochemicaUy generated polypyrrole films. J Electrochem Soc 128 2596-2599 Jaeger CD, Fan FRF, Bard AJ (1980) Semiconductor electrodes. 26. Spectral sensitization of semiconductors with phthalocyanine. J Am Chem Soc 102 2592-2598 Gerischer H (1977) On the stability of semiconductor electrodes against photodecomposition. J Electroanal Chem 82 133-143... 

Generally polypyrrole is prepared from electrolyte solutions employing organic solvents, but since the initial work by Diaz et al. [243-245,295], many workers have... 

Dynamic properties. On the basis of cyclic voltammetry, Diaz et al. (1981) showed that thin films of polypyrrole on an electrode immersed in acetonitrile could be repeatedly driven between the conducting and insulating states, as shown by the stability of the cyclic voltammograms of the films (see Figure 3.73). 

Figure 3.7J Cyclic voltammograim of a 20 nm-thick polypyrrole on Pi in letraelhylummonium lelrafluoroboraic CH,CN solution. The scan rales arc as shown. From Diaz i i at. (1981).

There is no doubt that doped polypyrrole is very much more stable than is polyacetylene, but reports are variable of exactly how stable it is. Street 393) reported that the polymer loses less than 20% of its initial conductivity after one year in air at ambient temperature and Diaz and Kanazawa 589) claimed that the polymer is stable at 100-200 °C, depending on the counter-ion the latter authors also reported that polypyrrole is undoped reversibly by ammonia treatment. Munstedt 590) found that the conductivity of doped polypyrrole was unchanged after 200 days at 80 °C in... 

Status of Polypyrrole. Polypyrrole (Diaz, 1981) has been examined and analyzed more than other electronically conducting organic polymers. It is the archetype of this class of compound. 

Polymers in this category are of interest in that they can be easily synthesized, being of very high stability. A couple of these polymers are illustrated in Fig. 16. Poly(p-phenylene) is prepared by the polymerization of benzene with A1C13 and CuCl2 (Kovacic and Kyriakis, 1963 Kovacic and Oziomek, 1964), whereas polypyrrole and polythienylene are prepared by the electrochemical polymerization of each monomer with an appropriate electrolyte (Diaz et al., 1979 Tourillon and Gamier, 1982). Polythienylene is also synthesized by the polycondensation of dihalo-thiophene (Yamamoto et al., 1980). 

Polypyrrole (PPy) was first prepared electrochemically at a platinum electrode in acetonitrile by Diaz et al, [20] which was followed by a few related works from the same group [21]. A stoichiometry similar to reaction (I) was presented for the preparation of neutral PPy in aqueous media by Pletcher et al [22]. These authors invoked an initial coupling mechanism in which an electrochemically generated radical cation couples with a neutral pyrrole molecule to produce a dimer radical cation, which is then further oxidized... 

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... 

Polypyrrole can be synthesized by both electrochemical and chemical methods. Although the synthesis of polypyrrole has been described before, studies on the electrochemical properties of polypyrrole intensified after Diaz et al [32] reported high-quality polypyrrole film electrochemically obtained by improving Dall Olio s method. 

Chromatic changes caused by electrochemical processes were originally described in the literature in 1876 for the product of the anodic deposition of aniline [271]. However, the electrochromism was defined as an electrochemically induced phenomenon in 1969, when Deb observed its occurrence in films of some transition metal oxides [272]. Electrochromism in polypyrrole was first reported by Diaz et al. in 1981 [273]. Electrochromism is defined as the persistent change of optical properties of a material induced by reversible redox processes. Electronic conducting polymers have been known and studied as electrochromic materials since the initial systematic studies of their electronic properties. 

M. Salmon, A. F. Diaz, A. J. Logan, M. Krounbi, J. Bargon, Chemical modification of conducting polypyrrole films, Molecular Crystals and Liquid Crystals 1982, 83, 1297. 

In 1979 [10] researchers at IBM in San Jose, led by Diaz, reported that polypyrrole (PP) could be obtained as a freestanding film by electrochemical oxidation of pyrrole in acetonitrile. The polymer was produced at the electrode surface and could be peeled off as a flexible, relatively dense, shiny, blue-black film. Polypyrrole had been already synthesized electrochemically from aqueous sulfuric acid solutions in 1969 by Gardini and co-workers [11], but the poor mechanical and electrical properties of the material obtained discouraged further developments of this synthetic method. 

Diaz, A. F., and Kanazawa, K. K., Polypyrrole an electrochemical approach to conducting polymers. Extended Linear Chain Compounds (J. S. Miller, ed.). Plenum Press, New York, 1982, pp. 417-441. 

Finally, an examination of the chronocoulometric data for polypyrrole presented in the literature clearly shows that these data do not conform to simple theory (25). Note, for example, that Diaz et al. show Q vs. plots with negative intercepts furthermore, the slopes of these plots increased as the positive limit of the potential step increased. We have obtained identical data in our laboratory (40). 

Dapp values for three different polypyrrole film thicknesses are shown in Table I. Each app i epi esents an average of eight determinations (two films, four different current densities for each film). Note first that the D pp values reported in Table I are as much as an order of magnitude larger than values reported by Diaz et al. (25) and Osaka et al. (29). Because these previously reported data were obtained using large amplitude chronoamperometric methods, we believe (see Theory Section) that these Dapp values are suspect. 

Polypyrrole and polythiophene, both first described in 1963 as electrically conducting materials [la], experienced a renaissance when Diaz and Street gave new attention to the electrochemical oxidation of pyrrole [21], and Gamier to the polythiphene field transistor. Polyphenylene vinylene, polyaniline, polyphenylene sulfide, polycarbazole, polyindole, polypyrene and polyene fulvene are just a few of the large number of electrically conducting polymers with specific properties and interest [22]. 

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