Polyanilines, synthesis aniline monomers

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. 

Materials studied are polyaniline, poly(3-octylthio-phene)(POT), and mixtures of poly(3-octylthiophene) (POT) and poly(ethylvinylacelate) (EVA). The synthesis of polyaniline was carried out by oxidation of aniline monomer using (NH4)2S20g in HCl (1 M) -I-HBF4 (1 M) or in the eutectic NH4F, 2.35 HF as... 

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. 

Synthesis of polyaniline is most often achieved through the direct polymerization of commercially available aniline monomers. Synthesis is usually performed in acidic media to yield the doped ES form of PANI that are coupled in the para - as opposed to ortho or meta - positions. The direct syntheses of... 

Template-guided synthesis 2,4) is currently being used increasingly to synthesize water soluble polyaniline. Apofyadd is used as a tenq>late to bind the aniline monomers to form the corresponding anilinium salt. Aniline monomers polymerize to form a conq)lex with the template. The hydrophobic and hydrophilic ends of the tenq)late he in sohibifizing the hydrophobic polyaniline chains. Some of the pofyadds used (25) in the synthesis of polyaniline are polystyrenesulfonic add, poly(aci dic add) and poly(methacrylic acid). 

The poly aniline nanospheres (PANI-NS) were synthesized by oxidative polymerization of aniline monomer at 0 °C in an ice bath using ammonium persulfate as the oxidant in the presence of surfactant. Aniline, ammonium persulfate, Polyvinylpyrrolidone, cetyl ammonium bromide, and camphorsulfonic acid are used as received from Sigma-Aldrich. Camphorsulfonic acid surfactant as the dopant and ammonium persulfate as the oxidant were used in the present synthesis of polyaniline nanospheres (see flow chart in Fig. 8.11). Calculated quantities of aniline monomer (0.005 mol) were mixed with 50 mL of distilled water and stirred using magnetic stirrer for 10 min. Meanwhile, calculated quantities of surfactant (0.75 mol) and oxidant (0.005 mol) were dissolved separately in distilled water and stirred for 10 min in an ice bath. The surfactant solution was first added to the aniline monomer aqueous solution, and then the previously cooled oxidant solution was added drop wise after which the mixture was allowed to react for 10 h in an ice bath. The precipitate was filtered and washed several times with distilled water and... 

As with the chemically grown nanofibers, the polyaniline nanofibers (PANI-NF-ES) were grown by oxidative polymerization of aniline monomer at 0 °C in an ice bath using ammonium persulfate as the oxidant in the presence of surfactant, though with slightly different conditions. Aniline, ammonium persulfate, dodecyl benzene sulfonic acid, acrylmethylpropyl sulfonic acid, and camphorsulfonic acid are used as received from Sigma-Aldrich. Sulfonic acid-based surfactants as the dopant and ammonium persulfate as the oxidant were used in the present synthesis of polyaniline nanofibers. 

Completely different monomers were called for. Before long, three of today s workhorses had been identified pyrrole, aniline and thiophene. In Japan, Yamamoto [38] and in Germany, Kossmehl [39] synthesized polythiophene doped with pentafluoroarsenate. At the same time, the possibilities of electrochemical polymerization were recognized. At the IBM Lab in San Jose, Diaz used oxidative electrochemical polymerization to prepare polypyrrole [40] and polyaniline. [41] Electrochemical synthesis forms the polymer in its doped state, with the counter-ion (usually an anion) incorporated from the electrolyte. This mechanism permits the selection of a wider range of anions, including those which are not amenable to vapor-phase processes, such as perchlorate and tetra-fluoroborate. Electrochemical doping also overcomes an issue associated with dopants... 

Ternary composites with electroactive components were also discussed by Gomez-Romero and coworkers in one of their recent publications [48]. The ternary composites consisted of doped-polyaniline (PANI) or doped-polypyrrole (Ppy) intercalated into V2O5 xerogels. The dopant anion for the conducting polymers was [Fe(CN)g] (HCF), derived from H3Fe(CN)6. More specifically, the synthesis of Ppy/HCF/V205 and PANI/HCFA 20s was carried out by treating the monomer (aniline or pyrrole)... 

Aniline was the first example of the conjugated polymers doped by proton, it can be chemically oxidized by ammonium peroxydisulfate (APS). PANI has the advantages of easy synthesis, low-cost, proton doping mechanism, and is controlled by both oxidation and protonation state. Polyanilines are commonly prepared by the chemical or electrochemical oxidative potymerization of the respective monomers in acidic solution. But, other potymerization techniques have also been developed, including ... 

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