Oxidative Polymerization of Aniline

Importantly, deep oxidation of polyaniline leads to a material that becomes insulating and spinless. This phenomenon was demonstrated in case of poly(fV-methylaniline) by monitoring ESR signal and electric conductivity of the sample (Wei et al. 2007). Deep oxidation results in the formation of the so-called polaron pairs that are evidenced by optical spectra. Because the hopping probability of two polarons on a single chain is too small, polaron pairs do not contribute to electric conductivity and ESR signal. 

The polymer resulting from oxidation of 3,5-dimethyl aniline with palladium was also studied by transmission electron microscopy (Mallick et al. 2005). As it turned out, the polymer was formed in nanofibers. During oxidative polymerization, palladium ions were reduced and formed palladium metal. The generated metal was uniformly dispersed between the polymer nanofibers as nanoparticles of 2 mm size. So, Mallick et al. (2005) achieved a polymer- metal intimate composite material. This work should be juxtaposed to an observation by Newman and Blanchard (2006) that reaction between 4-aminophenol and hydrogen tetrachloroaurate leads to polyaniline (bearing hydroxyl groups) and metallic gold as nanoparticles. Such metal nanoparticles can well be of importance in the field of sensors, catalysis, and electronics with improved performance. 

It is well known that phosphites or sulfides added to stabilizers of polymeric materials considerably enhance the stabilizing effects. Destruction of polymers is caused by the action of peroxides resulting from oxidation at the defects of polymeric chains. The additives decompose hydroperoxides according to the following equations  

While investigating the mechanism, Pobedimskii and Buchachenko (1968a, 1968b) concluded that these reactions have an ion-radical nature and consist of electron transfer from phosphites or sulfides (denoted further as D) to hydroperoxides as follows  

As noted, the products of electron transfer retained in the solvent cage. Benzene was used as a solvent in these experiments. The cage complex [R -O, OH, D+ ] decays either on disproportionation in the cage or dissociation. Disproportionaton leads to phosphinoxides or sulfoxides mentioned earlier. Dissociation results in the passage of radicals out of the cage into the solvent pool. 

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The use of conjugated polymer as membranes to separate various liquid mixtures has been reported in the literature [19,20], From those, polyaniline (PANi) is one of the most interesting and studied conjugated polymers. Polyaniline is usually prepared by direct oxidative polymerization of aniline in the presence of a chemical oxidant, or by electrochemical polymerization on different electrode materials [21,22], The possible interconversions between different oxidation states and protonated and depronated states [23], figure 4, make this material remarkable for different purposes. Under most conditions, PANi... 

Poly (anil i n e - 2-c h Ion tan i line) -p -toluenesulfonic acid salt was obtained by oxidative polymerization of aniline with o-chloroaniline in solutions containing p-toluenesulfonic acid. The copolymer salt was subjected to heat treatment under nitrogen atmosphere at elevated (about 150°C) temperatures. The heat-treated samples acquired electric conductivity 2.7 X 10-2 (1 em According to ESR spectra, the heated poly(aniline-2-chloroani-line)-p-toluenesul Ionic salt exists as the poly(semiquinone cation radical), in which unpaired electrons are localized on or near the nitrogen atoms (Palaniappan 1997). 

In addition to creating semiconductor or metal replicas of the channels of mesoporous materials, which are expected to display electron and hole quantum confinement effects, forming fibers of polymers could lead to materials with novel electrical, magnetic, optical or mechanical properties. To this end, oxidative polymerization of aniline within the channels of mesoporous silica has been reported [91]. Convincing spectroscopic evidence for intrachannel polymerization of aniline to poly(aniline) was provided. Extracted polymer had a molecular weight considerably smaller than that of the bulk material under similar conditions indicative of a diffusion constraint imposed upon the polymerization and growth of monomer inside the channel space of mesoporous silica. 

A. Yasuda and T. Shimidzu, Chemical oxidative polymerization of aniline with ferric chloride, Polym. J., 1993, 25, 329. 

Polyaniline In situ suspension oxidative polymerization of aniline in the presence of TiO in aqueous solution Iprobenfos fungicide 254 [596]... 

Chemical Oxidative Polymerization of Aniline Hard (Physical) Template Methods... 

Large, colorless aggregates were observed by static and dynamic light-scattering measurements during the induction period of an oxidative polymerization of aniline with APS in dilute acidic aqueous solutions [177]. These aggregates are believed to be dianUinium peroxydisulfate ion clusters whose shape (rod-like) plays an important role in the initial formation of PANI-NFs. The formation of the interconnected, branched nanofiber networks by dilute polymerization was explained as follows [171]. Competition between a... 

Solid-State Mechanochemical Synthesis Facile template-free solid-state mechano-chemical synthesis of highly branched PANI-NFs with coralloid tree-like superstrueture, via the oxidative polymerization of aniline hydrochloride with FeCl3 6H2O, has been demonstrated [194]. The synthetic yield ( 8%) was comparable to that of the solution interfacial polymerization method. Solid-phase mechanochemical synthesis of branched PANI-NFs was also achieved by using anhydrous FeCl3 as the oxidant [195]. 

Miscellaneous Template-Free Methods Self-assembled PANI-NFs have been prepared by the oxidative polymerization of aniline with APS in an acidic aqueous solution in the presence of HCl [172,204—206], HCl and ethanol [207], HCl and colloidal Au particles... 

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