Polyanilines in solutions

Fig. 69. Maximum spectral changes during the doping of polyaniline in solutions of different pH. Spectra were obtained with the metal grid electrode of Fig. 68. (After [14]). Reprinted by permission of Springer Verlag.

The solubility in concentrated sulfuric acid allows the investigation of the novel state of metallic chains of polyaniline in solution in sulfuric acid. Since the material should be fully protonated when in solution in sulfuric acid, this would be the first example of a metallic polymer as a "liquid metal". On the other hand, when in solution the interchain... 

As noted above, because of the reduced interchain electron transfer interaction for conjugated chains in solution, the electronic structure is expected to be more nearly onedimensional. Thus, the possibility of a Peierls transition with the formation of an energy gap in the excitation spectrum might be anticipated. The susceptibility results shown in Figure 9 suggest that this is indeed the case for polyaniline in solution in sulfuric acid. Such a large decrease in % cannot be accounted for in the context of the half-filled band expected for [B-NH-B-NH-]+n- To reduce X by such a large factor would require an increase in the band width by the same factor i.e. to a band width of more than 200 eV ... 

Cao, Y, and Heeger, A. J., Magnetic susceptibility of polyaniline in solution in nonpolar organic solvents and in polyblends in poly(methylmethacrylate), Synth. Met., 52, 193-200 (1992). 

Although a stiff chain conformation of polyaniline in solution in sulfuric acid is consistent with the conclusions inferred from the magnetic susceptibility data [46], the absence of evidence of liquid crystallinity for polyaniline in sulfuric acid suggests a more flexible chain conformation. On the other hand, the strong interchain electron transfer interactions inherent to n-conjugated polymers may lead to crystallization (and precipitation) rather than liquid crystal formation. 

Polyaniline (PANI) was investigated as electrocatalyst for the oxygen reduction reaction in the acidic and neutral solutions. Galvanostatic discharge tests and cyclic voltammetry of catalytic electrodes based on polyaniline in oxygen-saturated electrolytes indicate that polyaniline catalyzes two-electron reduction of molecular oxygen to H2O2 and HO2". 

Boyle A, Genies EM, Lapkowski M. Application of electronic conducting polymers as sensors— polyaniline in the solid-state for detection of solvent vapors and polypyrrole for detection of biological ions in solutions. Synth Met 1989 28 C769-C774. 

Figure 13.6 In situ infrared reflectance spectra of polyaniline-modified electrodes in solution containing 0.10 M HC1. Spectra collected at applied potentials indicated at right of curves, and normalized according to Eq. 13.12 using R0 collected at -0.1 V. Potentials measured against saturated calomel electrode. [From Ref. 54.]...

Sample Preparation. Chemically polymerized 2-ethyl polyaniline, with reported molecular weight of 5000, was prepared by the method outlined by Leclerc et al. (15). Treatment of the insoluble product with ammonium hydroxide solution resulted in transforming the salt into the soluble EB form, which exhibited slight solubility in methanol. The soluble EB form of PANi is known to be readily protonated under acidic conditions, producing the highly insoluble ammonium salt form (16.17). In order to maintain the free amine base form in solution, it was necessary to synthesize the silica gel in the presence of a minimal amount of acid catalyst. 

Below are reported comparisons of the model with some experimental systems. We consider successively the behaviour of a highly conductive polymer like polyaniline in contact with solutions containing redox couples (Fe(CN6)3 /Fe(CN6)4 ) and the oxidation of hydroquinone (HQ) mediated by a moderately conductive polymer (pECBZ) film. 

A few other types of anion sensors have been mentioned recently in the literature. Tetrathiofulvalene microcrystals immobilised at a platinum electrode displayed electrochemical properties that were affected by the presence of anions in solution, with some selectivity for anions such as bromide [ 145]. A flow-injection analysis system using anion-exchange columns for separation and polyaniline electrodes as detectors could detect dichromate down to 0.004 ppb and could be used for seawater samples [146]. 

A synthetic protocol for the formation of conducting filaments of polyaniline in the 3 nanometer wide channels of the aluminosilicate MCM-41 was developed (Figure 11).1°° Aniline vapor was allowed to diffuse into the dehydrated channels of the host at room temperature, followed by immersion into an aqueous solution of peroxydisulfate at 273 K. This reaction produced encapsulated polyaniline filaments. Spectroscopic evidence including UV-VIS and infrared data showed that the filaments are in the protonated emeraldine salt form (for example, Raman spectra exhibit modes indicative of the protonated quinone radical cation structure). A single, rather broad (8 G) electron spin resonance line (for an evacuated sample), at g = 2.0032 suggested slightly lower... 

Ito and co-workers prepared pseudopolyrotaxanes from polyaniline with emeraldine base and /f-cyclodextrin, which were studied by frequency-do-main electric birefringence (FEB) spectroscopy in a solution of N-methyl-2-pyrrolidone (NMP), scanning tunneling microscopy, etc. [120, 121]. The FEB results showed that polyaniline in the solution with cyclodextrin changed its conformation from coil to rod at low temperature below 275 K. Some rod-like structures were observed on a substrate by STM. Thus, the pseu-... 

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

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