Chemical synthesis of polypyrrole

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). 

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

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

Shi W., Liang P, Ge D., Wang J. and Zhang Q. (2007). Starch-assisted synthesis of polypyrrole nanowires by a simple electrochemical approach. Chemical Communications, (23), 2414-2416. 

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

Polypyrrole can be synthesized by both electrochemical and chemical methods. Although the synthesis of polypyrrole has been described before, studies on the electrochemical properties of polypyrrole intensified after Diaz et al [32] reported high-quality polypyrrole film electrochemically obtained by improving Dall Olio s method. 

Pyrrole was first polymerized in 1916 [1,2] by the oxidation of pyrrole with H2O2 to give an amorphous powdery product known as pyrrole black. However, little further interest was shown in this material until it was electrochemically prepared in the form of continuous films. The electrochemical synthesis of polypyrrole dates to the early work of DalTOllio [3], who also obtained pyrrole blacks by electrochemical oxidation of pyrrole in aqueous sulfuric acid on a platinum electrode. In 1979 [4] electrochemical techniques to synthesize polypyrroles become a useful way to obtain highly conductive free-standing materials. Chemical and electrochemical methods of synthesis have since then been improved in order to optimize the physical and chemical properties of those materials. 

The second problem associated with electrochemical synthesis of polypyrroles seems to be related to die difficulties found in correlating the polymer s properties with the conditions of synthesis. This has been derived from the widely spread idea of an overall understanding of the electrochemical mechanism. However, even the most simple electrochemical process of pyrrole electropolymerization involves different experimental variables in order to optimize polymer properties. These variables can be chemical, such as solvent or reactants (monomer and dopant salt), or physical, such as temperature, nature and shape of die electrodes, cell geometry or electrical conditions during synthesis. In addition, commonly the effects of all these variables are interdependent. 

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... 

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... 

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. 

The discovery that doped forms of polypyrroles conduct electrical current has spurred a great deal of synthetic activity related to polypyrroles [216-218], Reviews are available on various aspects of the synthesis and properties of polypyrroles [219,220]. In addition, summaries of important aspects of polypyrroles are included in several reviews on electrically conducting polymers [221-226]. Polypyrrole has been synthesized by chemical polymerization in solution [227-231], chemical vapor deposition (CVD) [232,233], and electrochemical polymerization [234-240]. The polymer structure consists primarily of units derived from the coupling of the pyrrole monomer at the 2,5-positions [Eq. (84)]. However, up to a third of the pyrrole rings in electrochemically prepared polypyrrole are not coupled in this manner [241]. 

Several mechanisms have been proposed for both electrochemical and chemical oxidative synthesis of poly thiophenes. The proposed mechanisms are similar to those proposed for polypyrrole formation. The first step of the polymerization is the oxidation of the thiophene monomer to a cation radical. The subsequent steps are controversial. There are several possibilities. The cation radical can couple with another cation radical or with a neutral species. Alternatively, the cation radical can deprotonate to form a neutral radical. This radical can then couple with another radical or with a neutral species. Several of these possibilities are discussed below. 

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