Polyanilines, synthesis chemical polymerization

Figure 14.7 TEM ofPANI hollow spheres produced by chemical polymerization of aniline on polystyrene particles and removal with tetrahydrofuran, and decorated with gold nanoparticles. (Reprinted with permission from Langmuir, Polyaniline / Au composite hollow spheres Synthesis, characterisation, and application to the detection of dopamine by X. M. Feng, C.J. Mao, C. Yang et al., 22, 9, 4384-4389. Copyright (2006) American Chemical Society)...

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-... 

Electroactive polyaniline films were synthesized by the catalysis of biUru-bin oxidase (BOD, a copper-containing oxidoreductase). The polymerization of aniline was carried out on the surface of a sohd matrix such as glass sUde, plastic plate, or platinum electrode to form homogeneous films [33]. The BOD was immobilized on the surface by physical absorption. The optimum pH was around 5.5. Some aniline derivatives such as p-aminophenol and p-phenylenediamine were good substrates for BOD. Structural analysis suggested the BOD synthesized polyanihne possessed partially 1,2-substititued structures. Cyclic voltammetric studies demonstrated that the PANl films were electrochemically reversible in redox properties, but differed from that of chemically or electrochemically synthesized PANl. The difference was attributed to the partial 1,2-substitution. Laccases are known to oxidize phenolic compounds in nature in the presence of oxygen and are capable in polyaniline synthesis in vitro [34-36]. 

The inter-relationship between colloid and polymer chemistries is completed by colloidal polymer particles. The formation of 50-nm-diameter, 100- to 200-nm-long polyaniline fibrils in a poly(acrylic acid)-template-guided polymerization, similar in many ways to those produced from polymerized SUVs (see above), provides a recent example of polymer colloids [449], The use of poly(styenesulfonic acid) as a template yielded globular polyaniline particles which were found to be quite different morphologically from those observed in the regular chemical synthesis of polyaniline [449]. 

The emeraldine salt of polyaniline which is one of the three different forms of polyaniline—leucoemeraldine (the fully reduced state], emeraldine (the half oxidized state] and pernigraniline (the fully oxidized state] (Fig. 8.1]—is electrically conductive while the others are insulators. Conventional chemical synthesis of polyaniline is based on an oxidative polymerization of aniline by using an oxidant in the presence of a strong acid dopant in the reaction mediunL ... 

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. 

Leclerc [125] has shown that poly(2-methyl aniline) has properties similar to that of polyaniline. Dao et al. [127] have carried out extensive investigations on chemical and electrochemical polymerization of substituted polyanilines. These authors report that chemical synthesis yields a polymer having a higher molecular weight. Some of their results are given in Table 12.13. Their study further shows that there is no polymer film on an electrode surface in the presence of the following substitutions ... 

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