Doping of polypyrrole

Hutchins RS, Bachas LG. Nitrate-selective electrode developed by electrochemically mediated imprinting doping of polypyrrole. Anal Chem 1995 67 1654-1660. 

M.D Levi, C. Lopez, E. Vieil, and M.A. Vorotyntsev, Influence of ionic size on the mechanism of electrochemical doping of polypyrrole films studied hy cyclic voltammetry, Electrochim. 

Figure 1.50. Creation of polarons and bipolarons in electrochemical doping of polypyrrole. (Reprinted with permission from ref. 109)...

Apart from metallic salts, simultaneous chemical synthesis and doping of polypyrrole has been achieved by an halogenic electron acceptor, as bromine or iodine, in several solvents [27-31]. Both PPy-l2 and PPy-Br2 complexes have conductivities in the order of 1 to 30 S cm [30]. PPy-Cl2 prepared polymers have conductivities from 10 to 0.5 S cm [27]. The loss of conductivity with respect to PPy-Br2 or PPy-h has been associated with a partial chloration of the pyrrole ring, with some loss of conjugation. Both PPy-l2 and PPy-Br2 complexes show a good stability upon repeated redox cycling in both aqueous and organic electrolytes [31]. 

Pyrrole has been also oxidized by means of halobenzoquinones [32,33]. The electrical conductivity of the polypyrrole-chloranil complex is about 2 to 10 S cm while for the PPy-pfluoranil and PPy-[a-bromanil complexes it is in the range of 10 to 10 S cm . Synthesis and doping of polypyrrole has been performed by 2,3-dichloro-5,6-dicyano-/ -benzoqui-none (DDQ) and tetrachloro-o-benzoquinone from bulk polymerization [34]. The polypyrrole complexes so produced are semiconducting and granular, with electrical conductivities of the order of 10 to 10 S cm . ... 

The choice of an appropriate electrolyte for the doping of polypyrrole during electrochemical polymerization can improve the mechanical properties of the films obtained. Thus, polypyrrole films electrogenerated in the presence of large electrolytes, as /7-toluensulpho-nate, tosylate, benzene sulfonate, etc., yield flexible films with tensile strengths similar to polystyrene [113]. We can extrapolate this behaviour by combining the... 

Significant variations in the properties of polypyrrole [30604-81-0] ate controlled by the electrolyte used in the polymerization. Monoanionic, multianionic, and polyelectrolyte dopants have been studied extensively (61—67). Properties can also be controlled by polymerization of substituted pyrrole monomers, with substitution being at either the 3 position (5) (68—71) or on the nitrogen (6) (72—75). An interesting approach has been to substitute the monomer with a group terminated by an ion, which can then act as the dopant in the oxidized form of the polymer forming a so-called self-doped system such as the one shown in (7) (76—80). 

Fig. 5. Evolution of optical spectra of polypyrrole during electrochemical doping.

FIGURE 4-22 Typical response of polypyrrole detector to carbonate (S , 1 x 10-4M S2,2.5x lO M S3, 5 x 10 m) based on the doping-undoping process. (Reproduced with permission from reference 74.)... 

Mogi, I., Watanabe, K and Motooka, M. (1999) Effects of magnetoelectropolymerization on doping-undoping behavior of polypyrrole. Electrochemistry,67,1051—1053. 

As might be expected, the properties of polythiophene show many similarities with those of polypyrrole. As with polypyrrole, polythiophene can be prepared via other routes than electrochemical oxidation both as the neutral material [390-392] or in the p-doped form [393]. This material is produced as an infusible black powder which is insoluble in common solvents (and stable in air up to 360°C), with conductivities ranging from approximately 10 11 Scm-1 in the neutral form [390] to 102 Scm-1 when doped [19, 393, 394]. Early work on thiophene polymers showed that the p-doped material is air-sensitive in that the conductivity decreases on exposure to the atmosphere [20, 395] although no evidence of oxygen-containing species was seen in XPS measurements [19],... 

Further studies by this group centered on comparisons of the overoxidation resistance limit (ORL) of polypyrrole materials doped with monoanionic borane clusters [B12H11NH3] or dianionic borane [B12H12]2 or carborane [Co(C2B9Hu)2]2-clusters. The monoanionic boron clusters were found to offer the highest stability to the PPy doped materials against overoxidation than any other charged dopant. They were also found to be far superior to the dianionic clusters in their ability to impart an ORL rise.140... 

Both approaches suffer from the high susceptibility of polypyrrole to oxidation by even trace amounts of oxygen. The latter method has the disadvantage that the comparison of the absorbances at different doping levels has to... 

In 1983, Yakushi et ai obtained UV-visiblc spectra of polypyrrole at various doping levels via the second approach described above and the results are shown in Figure 3.71. The authors employed a two-electrode cell and hence the potentials quoted are the potentials between the working and counter electrodes prior to removing the film. 

A.A. Karyakin and M.F. Chaplin, Polypyrrole-Prussian Blue films with controlled level of doping codeposition of polypyrrole and Prussian Blue. J. Electroanal. Chem. 370, 301-303 (1994). 

Following the discovery of the unique electronic properties of polypyrrole, numerous polymers of pyrrole have been crafted. A copolymer of pyrrole and pyrrole-3-carboxylic acid is used in a glucose biosensor, and a copolymer of pyrrole and A-methylpyrrole operates as a redox switching device. Self-doping, low-band gap, and photorefractive pyrrole polymers have been synthesized, and some examples are illustrated [1,5]. 

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