Synthesis polyaniline

Jim Z, Su Y, Duan Y (2001) A novel method for polyaniline synthesis with the immobilized horseradish peroxidase enzyme. Synth Met 122(2) 237-242... 

The mechanism of polyaniline formation is an area of active research and controversy. The wide range of reaction conditions used in polyaniline synthesis and the resulting differences in the structure and characteristics of the polymers has probably contributed to the proposal of many different mechanisms. The majority of the proposed mechanisms begin with the oxidation of aniline to a cation radical (445). Two of these cation radicals couple to form /V-phenyl-p-phenylenediamine (443). The oxidation of the aniline monomers to form dimeric species is the slow step in the polymerization [271,285,286]. The subsequent steps of polymer growth are under discussion. 

Thus a rather simple C NMR spectrum is expected for polyleucoemeraldine. In Figure 4.5 a NMR spectrum of chemically prepared polyleucoemeraldine, dissolved in 50/50 v/v mixed solution of NMP and deuterated dimethylsulphoxide (dg-DMSO) is presented. Two major peaks in the chemical shift region corresponding to aromatic carbons can be observed at 117.8 ppm and 137.4 ppm. If the spectrum is recorded under quantitative conditions, the intensity ratio of both peaks is 2 1 and these two peaks account for more than 95% of the intensity in the quantitative spectrum. In addition to these dominant spectral lines corresponding to C(l) and C(2) respectively, several peaks of low intensity are recorded which are associated with polyleucoemeraldine chain defects of various types. However, recent improvement in polyaniline synthesis resulted in C NMR spectra in which these peaks are practically non-existent [52],... 

M. Malta, G. Louam, N. Errien, and R. M. Torresi, Nanofibers composite vanadium oxide/ polyaniline synthesis and characterization of an electroactive anisotropic structure, Electrochem. Commun., 5, 1011-1015 (2003). 

Sun, Y, Macdiarmid, A. G., and Epstein, A. J. Polyaniline synthesis and characterization of pemigranihne base. Journal of the Chemical Society, Chemical Communications, 7, 529-531 (1990). 

Figure 7.50 shows the meta- and ortho-polytoluidine products a week after polymerization. The reaction conditions were identical for the two reactions, but there is a big difference in the volume occupied by the polymer (Figure 7.50, insets). Based on the experience obtained with polyaniline synthesis (Figure 7.14) this indicates a big difference in the morphology of the products (see Section 7.2.4). For example, m-polytoluidine occupies much more volume than o-polytoluidine. Electron... 

The preponderance of patent or sdentific literature regarding polyaniline synthesis in aqueous media reports synthetic conditions whereby the concentration of the acid is measurable on the pH scale and the acid most frequently reported is HCl. The activity and concentration of the hydronium ion are obtained by measurements of pH by ion-selective electrodes or pH paper-containing indicators. However, such pH measurements are valid only in single-solvent systems, typically water, for very dilute concentrations of an acid. However for very concentrated add solutions, such as those used to polymerize aniline at subzero temperatures, the preferred measure of the ability of an acid to dissociate a proton from an indicator, according to HB+ H+4-B, is the Hammett acidity function, Hq given by... 

MacDiarmid, A.G., J.C. Chiang, A.E Richter, N.L.D. Somasiri, and A.J. Epstein. 1987. Polyaniline Synthesis and characterization of the emeraldine oxidation state by elemental analysis. In Conducting polymers, Ed. L. Alcacer. Dordrecht, Holland Riedel Publishers. 

A. A. Karyakin, I. A. Maltsev, L. V. Lukachova, The influence of defects in polyaniline structure on its electroactivity optimization of self-doped polyaniline synthesis, /oarwit/ of Electroanalytical Chemistry 1996, 402, 217. 

The second important aspect of polyaniline synthesis is the acid dissociation constant (pA a) of the acid, because in polyaniline protonation equilibria involves exclusively the quinone diamine segment, having two-imine nitrogen with pATai = 1 -05 and pK 2 — 2.55 [20]. Therefore any acid whose value falls within that range would be suitable as a dopant (Table 12.2) whereas the anilinium ion has a pK of 4.60 and the ammonium ion 9.24. 

A variety of oxidants have been used to elfect chemical polymerization of aniline under acidic conditions, pH 1-3. It is very strange to note that there is no relationship between the oxidation potential of the reagent and the polymer yield however, our experience in polyaniline synthesis suggests that a simple oxidizing agent like ammonium peroxydisulphate yields a polymer of better quality than oxidizing agents contain-... 

During the electrosynthesis of polyaniline these authors noted that (after initial polymerization) the potential of the electrode has to be increased to continue polymerization. This suggests that polyaniline synthesis under these conditions has no autocatalytic activity. 

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