Polypyrroles - Chemical Syntheses

The chemical synthesis of Polypyrrole-themio-plastic powder blend [127]. 

J. Duchet, R. Legras, and S. Demoustier-champagne, Chemical synthesis of polypyrrole stmeture-properties relationship, Synth. Met., 98, 113 122 (1998). 

Figure 18.7 Chemical synthesis of CP by oxidative coupling (A) apparatus and (B) example of conventional reaction for fabrication of polypyrrole (PPy)...

Warren, L.R, and D.R. Strauss. 1989. Chemical synthesis of conducting polypyrrole using uniform oxidant/dopant reagents. US Patent 4,847,115. 

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. 

S. Rapi, V. Bocchi, G. P. Gardini, Conducting polypyrrole by chemical synthesis in water, Synthetic Metals 1988, 24, 217. 

The chemical synthesis and electrosynthesis of polypyrrole in the presence of sulfonated cyclodextrin as a dopant has been reported (52). In this case, cyclodextrin seems to play an important role in forming polymer with ordered structure. 

There are two main methods used to synthesize polypyrrole chemical and electrochemical polymerization. The principal advantage of chemical methods is related to the possibility of mass production at low cost. This is often difficult to achieve with electrochemical methods, although the continuous synthesis of electrochemically polymerized pyrrole has also been developed [5,6]. On the other hand, electrochemical methods offer materials with better conducting properties and for some applications such as the construction of electronic devices, electrochemical polymerization offers the possibility of in-situ formation. 

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]. 

The method of incorporation of ARs into the polymer matrix has been demonstrated by the polymerisation of pyrrole [118]. In the presence of protons, radical IV causes polymerisation of pyrrole to polypyrrole with the incorporated reduced (hydroxylamine) form and oxidised (nitrosonium ion) form of ARs in the polymer matrix. In electrochemical oxidation of pyrrole in the presence of ARs, a coupled electrochemical-chemical synthesis produces polypyrrole films with incorporated nitrosonium ions. They can by reduced to ARs by partial film reduction. 

Castillo-Ortega M, Inoue M, Inoue M (1989) Chemical synthesis of highly conducting polypyrrole by the use of copper (II) perchlorate as an oxidant Synth Met 28 65-70... 

Duchet J, Legras R, Demoustier-Champagne S (1998) Chemical synthesis of polypyrrole Structure-properties relationship. Synth Met 98 113-122... 

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... 

Besides synthesis, current basic research on conducting polymers is concentrated on structural analysis. Structural parameters — e.g. regularity and homogeneity of chain structures, but also chain length — play an important role in our understanding of the properties of such materials. Research on electropolymerized polymers has concentrated on polypyrrole and polythiophene in particular and, more recently, on polyaniline as well, while of the chemically produced materials polyacetylene stih attracts greatest interest. Spectroscopic methods have proved particularly suitable for characterizing structural properties These comprise surface techniques such as XPS, AES or ATR, on the one hand, and the usual methods of structural analysis, such as NMR, ESR and X-ray diffraction techniques, on the other hand. 

Thiophene, pyrrole and their derivatives, in contrast to benzene, are easily oxidized electrochemically in common solvents and this has been a favourite route for their polymerization, because it allows in situ formation of thin films on electrode surfaces. Structure control in electrochemical polymerization is limited and the method is not well suited for preparing substantial amounts of polymer, so that there has been interest in chemical routes as an alternative. Most of the methods described above for synthesis of poly(p-phenylene) have been applied to synthesise polypyrrole and polythiophene, with varying success. 

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