Acid Doping of Polyaniline

FIGURE 3.26. Reduced and oxidized states of a polymer blend consisting of a conjugated polymer (PMPy/PMPy — shaded bands) and an ionic polymer (PSS) with fixed electroinac-tive anionic charges (0) in a dilute electrolyte. In the oxidized state the polaronic sites are shown to be stoichiometrically charge-compensated by the PSS anions. Note that the polymer blend of Fig. 3.25 has not reached this oxidation state at 0.4 V/SCE. 

Second in the polymer matrix, the protonation/deprotonation of PANI-E proceeds 

According to Eqn. 35 (PANI-E)H constitutes a Br0nsted acid, for which the dissociation equilibrium was characterized by a value of pK 5/ Like the PMPy/PSS example, polyaniline can be prepared in the presence of poly(vinylsulfonate), PVS. Volta-potential experiments demonstrated that the produced PANI-E/PVS matrix constitutes a cation exchanger, also in the protonated state. The protonation/ deprotonation equilibrium in the PANI-E/PVS matrix is illustrated in Fig. 3.31. 

It is important to consider that the protonation/deprotonation equilibrium involves the concentration (activity) of protons in the polymer. However in experiments the activity of i.e., the pH of the bathing solution, is controlled. Therefore the membrane state of the polymer, i.e., the Donnan potential, which affects the peutitioning 

FIGURE 3.27. Results of Volta-potential measurements on an emersed electrode coated with poly[(pyrrole)ii-co-N-sulfopropylpyrrole]. The is the Volta-potential 

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FIGURE 15.1 (continued) (c) protonic acid doping of polyaniline. 

M. Angelopoulos, N. Patel, R. Saraf, Amic acid doping of polyaniline-characterization and resulting hlends, Synthetic Metals 1993, 55, 1552. 

Chiang J, MacDiarmid AG (1986) Polyaniline protonic acid doping of the emeraldine form to the metallic regime. Synth Met 13 193-205... 

The emeraldine salt, (II-7), can also be obtained directly from leucoemeraldine by charge transfer doping, with reactions analogous to (II-1) and (II-3). Thus, the doping of polyaniline has been described as two-dimensional in a space where one axis describes the charge transfer chemistry and the second, orthogonal axis describes the acid/base (protonation) chemistry [37]. 

Chiang J. C. and MacDiarmid A. G., Polyaniline. Protonic acid doping of the emeral-dine form to the metallic regime, Synth. Met., 13, 193-197, 1986. 

Polyaniline holds a special position among conducting polymers in that its most highly doped form can be reached by two completely different processes protonic acid doping and oxidative doping. Protonic acid doping of emeraldine... 

J.-C. Chiang, A. G. MacDiarmid, Polyaniline Protonic Acid Doping of the Emeraldine Form to the Metallic Regime. Synth. Met. 1986, 13, 193-205. 

The doping of polyaniline [PANl) is done by protonation (using an acid), while with the other conjugated polymer it is achieved by electron transfer with a dopant or electrochemically (Fig 3.13 Emeraldine base (a), Emeraldine salt (b)). 

Figure 1.11 Oxidative and protonic acid (nonoxidative) doping of polyaniline.

S. A. Chen, G. W. Hwang, Water-soluble self-acid-doped conducting polyaniline - Structure and properties, Journal of the American Chemical Society 1995, 117, 10055. 

Figure 2.20 Synthesis mechanism of water soluble self-acid-doped sulfonated polyaniline. (Reprinted with permission from Macromolecules, 29, 3950. Copyright (1996) American Chemical Society.)...

In addition to sulfonic acid groups, carboxylic acid groups as ring substituents results in self-doping of polyaniline and influence properties such as solubility, pH dependent redox activity, conductivity, thermal stability, etc. Sulfonated polyanilines are typically obtained by postpolymerization modifications such as electrophilic and nucleophilic substitution reactions. However, carboxylic-acid-functionalized polyanilines are typically synthesized directly by chemical and electrochemical polymerization of monomer in the form of homopolymer or copolymer with aniline. In contrast to sulfonated polyaniline, very few monomers are available for the synthesis of carboxyl acid functionalized polyaniline. Anthranilic acid (2-aminobenzoic acid) is an important monomer and is often used for the synthesis of carboxyl acid functionalized polyanilines. 

Xia, Y, Wiesinger, J. M., MacDiarmid, A. G., and Epstein, A. J., Camphorsulfonic acid doped polyaniline emeraldine salt conformations in different solvents studied by a UV/visible/near-infrared spectroscopic method, Chem. Mater., 7, 443-445 (1995), Min, Y, Xia, Y, MacDiarmid, A. G., and Epstein, A. J., Vapor phase secondary doping of polyaniline, Synth. Met., 69, 159-160 (1995). 

The technique is very unlikely to have major industrial impact due to the toxicity of the solvent. On the other hand, doping of polyaniline with dodecylbenzenesul-fonic acid can be more attractive because the doped polymer can be processed from hydrocarbon solvents such as toluene and xylene. 

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