Polyaniline electrochemical synthesis

Wnek 180> proposed that the structure of the oxidized insulating form of conventionally formed polyaniline is approximately a 50 % copolymer of diamine and diimine units, corresponding to the emeraldine structure and Hjertberg et al.180 obtained CPMAS NMR evidence for this conclusion. Some confirmation of the structure has also been obtained by chemical synthesis of the polymer182). However, Kitani et al.183) have suggested that the normal electrochemical synthesis leads to partially cross-linked polymers. 

Sherman, B. C., W. B. Euler, and R. R. Force. 1994. Polyaniline—A conducting polymer electrochemical synthesis and electrochromic properties. Journal of Chemical Education 71 (4) A94-A95. 

Electrochemical synthesis of electroconducting polymers such as polyarene [28— 31], polypyrrole [32-34], polythiophene [35], and polyaniline [36, 37] has been carried out in moisture sensitive chloroaluminate ionic liquids. However, the polymer hlms are decomposed rapidly by the corrosive products like HCl generated by hydrolysis of the ionic liquids. In addition the treatment of the chloroalminate ionic liquids requires a special equipment such as glove box. 

In general, chemical oxidation provides ICPs as powders, while electrochemical synthesis leads to films. There is recent evidence [3] in the case of polyanilines that the materials formed via the chemical and electrochemical routes have different conformations for their polymer chains. 

The preparation of polypyrrole, polythiophene, polyaniline, and related conducting polymers demonstrates principles of electrochemical synthesis that are more widely applicable, and it is instructive to examine these in detail. 

In conclusion, a variety of parameters, whether they are internal or external to the aniline molecule, can affect the electrochemical synthesis of polyaniline as well as its physicochemical properties. By taking advantage of these effects, one can work out strategies to enhance the growth rate of the polymer and also modify the properties of the polymer in a desirable direction. 

Tiwari A. and Gong S. Q., Electrochemical synthesis of chitosan-co-polyaniline/ WO3 nH20composite electrode for amperometric detection of NOj gas. Electroanalysis, 20(6), 1775-1781, 2008. 

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... 

M. Delvaux, J. Duchet, P.-Y. Stavaux, R. Legras, and S. Demoustier-Champagne, Chemical and electrochemical synthesis of polyaniline micro- and nano-mbules, Synth. Met., 113, 275-280 (2000). 

JM. Kinyanjui, J. Hanks, D.W. Hatchett, A.J. Smith, and M. Josowicz, Chemical and electrochemical synthesis of polyaniline/gold composites, J. Electrocherru Soc., 151, D113MJ120 (2004). 

V. Tsakova, D. Borissov, and S. Ivanov, Role of the polymer synthesis conditions for the copper electrodeposition in polyaniline, Electrochem. Common., 3, 312-316 (2001). 

M. Ilieva, S. Ivanov, and V. Tsakova, Electrochemical synthesis and characterization of Ti02-polyaniline composite layers, J. Appl. Electrochem., 38, 63 9 (2008). 

Figure 14.9 The application of porous PAN films and composites to the sensing of nitrite. Scale 7 gm (A) Porous film ofpoly(aniline) formed from the in situ electrochemical synthesis in the presence of WO nm polystyrene nanoparticle templates. (B) Enhanced electrocatalysis of concentrations of 50 gM nitrite in 0.7 M HCI at+ 50 mVvs. Ag/AgCI of the nanocomposite film (d) compared to classy carbon (a), pre-treatedglassy carbon (b) and bulk PANI [85]. (Reprinted with permission from Chemistry A European journal, Nanocomposite and nanoporous polyaniline conducting polymers exhibit enhanced catalysis of nitrite reduction by X. Luo, A.j. Killard and M.R. Smyth, 13, 2138-2143. Copyright (2007) Wiley-VCH)...

Majidi, M.R., L.A.P. Kane-Maguire, and G.G. Wallace. 1998. Electrochemical synthesis of optically active polyanilines. Aust J Chem 51 23. 

Berlin et al. [166] reported the synthesis of n-doped polycationic polythiophenes using thiophene monomer functionalized with ammonium groups (see Figure 1.20 (7)). The polymer exhibits reversible p-and n-doping characteristics. The n-doping process and the associated expulsion of anions, is reportedly fast and independent of cation size, and the in situ conductivity is reportedly 2 x 10 S/cm. Kumar et al. synthesized a fully sulfonated n-doped polyaniline electrochemically using an acetonitrile-water (4 1) mixture [180]. The n-doping was confirmed... 

M. Lapkowski, Electrochemical synthesis of polyaniline poly(2-acryl-amido-2-methyl-l-propane-sulfonic acid) composite, Synthetic Metals 1993, 55, 1558. 

K. Krishnamooithy, A. Q. Contractor, A. Kumar, Electrochemical synthesis of fully sulfonated n-dopable polyaniline poly(metanilic acid), Chemical Communications 2002, 240. 

Apart from chemical synthesis, electrochemical synthesis is a versatile method for the preparation of self-doped sulfonated polyaniline in both soluble forms and thin films deposited on an electrode surface. Electropolymerization of sulfonated polyaniline homopolymers and copolymers has been carried out in aqueous and nonaqueous media. Similar to chemical synthesis, electrochemically controlled electrophilic and nucleophilic substitution reactions are also reported. 

Y. Sahin, K. Pekmez, A. Yildiz, Electrochemical synthesis of self-doped polyaniline in fluorosulfonic acid/acetonitrile solution, Synthetic Metals 2002, 129, 107. 

Similarly, self-doped PABA can be prepared using excess of saccharide and one equivalent of fluoride to monomer. Complexation between saccharides and aromatic boronic acids is highly pH dependent, presumably due to the tetrahedral intermediate involved in complexation [25]. Because the pKa of 3-aminophenylboronic acid is 8.75, complexation requires pH values above 8.6. This pH range is not compatible with the electrochemical synthesis of polyaniline, which is typically carried out near a pH value of 0. However, Smith et al. have shown that the addition of fluoride can stabilize the complexation of molecules containing vicinal diols with aromatic boronic acids [23]. Based on this work, it was postulated that the electrochemical polymerization of a saccharide complex with 3-aminophenylboronic acid in the presence of one molar equivalent of fluoride at pH values lower than 8 is possible if a self-doped polymer is produced in the process. 

A new class of water soluble polypyrrole has been prepared by selfdoping of the polymer. These self-doped polypyrroles can be prepared electrochemically or chemically, using various dopant anions covalently bound to the polymer backbone. The self-doped sulfonated polypyrrole is most commonly synthesized electrochemically in nonaqueous media. Electrochemical synthesis in aqueous media and chemical synthesis are not typically used, presumably due to issues with overoxidation. The postpolymerization modification of polypyrrole, in a manner similar to that used to form sulfonated polyaniline is rare [41]. The various synthetic approaches and properties of the polymer are discussed in the following sections. 

Aniline was first obtained in 1826 from the pyrolytic distillation of indigo and was found to produce crystalline salts with sulfuric and phosphoric acid. In 1840, a colorless oil was isolated from indigo and oxidized to polyaniline [124]. Letheby [1] reported the electrochemical synthesis of poly aniline in 1862 when he observed... 

Hoang, H.V. (2007) Electrochemical synthesis of novel polyaniline-montmorillonite nanocomposites and corrosion protection of steeL Unpublished Ph.D. dissertation, TU Chemnitz, Germany. 

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