Electrochemical polymerization of ring-substituted dimethylaniline was performed in aqueous acid solutions to obtain soluble conducting polyaniline. The conductivity values of polydimethylanilines obtained were in the range of 10-1- 10-7Scm-1 depending on the preparation conditions. The molar masses of the oxidation products were in the order of 10.3 gregardless of the monomer structure. These conductive oligomers were easily soluble in polar organic solvents. Soluble conducting oligomers were also obtained by chemical polymerization with iron (Ⅲ) species.

Electropolymerization of aniline in perchloric acid solutions was investigated with presence of para-phenylenediamine (PPDA). Experimental results showed that the presence of PPDA promoted markedly the growth of the polymer. The catalytic effect of PPDA on the polymerization of aniline included its contributions to both the autocatalysis and the external catalysis. Addition of PPDA with an appropriate concentration resulted a polymer with high polymerization degree and higher conductivity, which were closely related to the contribution of PPDA to the autocatalysis in the polymerization of aniline. Memory effects in and else properties of the catalytically electrosynthesized polyaniline were also studied,

In aqueous acidic solutions, a higher peak current and a more positive peak potential for the first oxidation peak of polyaniline (PAN) compared with those obtained in a multicycle voltammogram was observed after holding at a sufficiently negative potential. This is referred to as a memory effect in PAN. An exception to this behavior was observed at low scan rate, when the peak potential in the first voltammogram can be less positive than that in the multicycle voltammogram. When the solvent was substituted by a mixture of water and some organic solvents, the first oxidation peak obtained in aqueous solution split into two subpeaks. The first subpeak, with a less positive peak potential, contributed strongly to the memory effect observed in PAN, but the second subpeak, with a more positive peak potential, was little influenced by holding in the reduced state. The exception mentioned above could be explained in terms of the existence of these two subpeaks if it could be shown that they were present for PAN in any solvent. These two subpeaks may reflect different structures in reduced PAN or be due to solvent effects on PAN intermediates during cycling.

Electrochemical formation and overoxidation of polyaniline (PAn) were investigated in solutions containing different anions. The anions promoted PAn growth in the order, H2SO4>HCI>HCIO4. The growth rate of PAn in the presence of two different types of anion was governed by the anion with lesser promoting effect. The addition of a small amount of HCIO4 into the H2SO4 solution greatly inhibited the initial monomer oxidation and the growth of the polymer. Similar promoting/depressing effects of anions were observed on electrochemical degradation of PAn films. The effects of anions were possibly related to the stability of complexes between the anion and protonated monomer, and the anion and protonated PAn chains.

Electrochemical copolymerization of aniline and aniline-2,5-disulfonic acid (ADSA) was carried out in HCI solutions. The presence of ADSA inhibited significantly the growth of polyaniline (PAn), although the voltammetry of the copolymer was still similar to that of conventional PAn. As the ADSA concentration increased, the deposition rate of the copolymer decreased rapidly and finally no solid film was deposited on the electrode surface. When the ADSA concentration was lower than-5 mM, the depression effect of ADSA on the growth rate of the copolymer is mainly due to its stronger adsorption at the electrode surface. For higher ADSA concentrations, the inhibiting effect of ADSA was dominated by its termination effects, which led to more soluble oligomers and in turn resulted in lower deposition efficiency. Electrolysis of ADSA solution might result in a water-soluble fully sulfonated PAn. aniline, aniline-2,S-disulfonic acid, copolymerization, polyaniline, water-soluble

Electropolymerization of aniline-2,5-disulfonic acid in aqueous solutions results in formation of a water-soluble self-doped polymer. E€ects of synthesis conditions were investigated on conductivity and molecular-weight distribution of the polymer. The polymer shows solubility in water high up to 109 mg cm-3. The conductivity of the polymer, with best value of about 0.34 S cm-1, is independent on pH up to at least pH 9.

Self-doped polyanilines were electrochemically synthesized in aqueous acid solutions through the copolymerization of aniline (An) and aniline-2,5-disulfonic acid (ADSA) and the polymerization of ADSA alone. The voltammetry of the copolymers shows characteristics similar to those of conventional polyaniline (PAn), and the copolymers exhibit higher electrochemical activity at values of pH higher than about 4. The presence of ADSA inhibits significantly the growth of PAn. When the relative concentration of ADSA approaches unity, no solid film is able to deposit on the electrode surface. However, the polymerization of ADSA results in the formation of water-soluble poly-ADSA. Electric conductivities of poly-ADSA and poly-An-ADSA are in the magnitude of 10-1-10-2 and 10-0-101Scm-1, respectively, lower than that of conventional PAn, 10°-101S cm-1. The conductivity of poly-ADSA is found to show little pH dependence up to at least 9.

Electrochemical stability of polywtetraethyldisilanylene.oligo2,5-thienylene.x DSmT; m refers to the number of thienylene units. films is investigated by means of in situ UV-vis-NIR spectroscopy, in situ and ex situ fluorescence spectroscopy, gel-permeation chromatography, and FT-IR spectroscopy. It is found that a Si-Si bond in DSmT film with ms3 to 5 is cleaved at potentials as low as 0.5 V versus AgrAgq in acetonitrile, resulting in dissolution of oligothiophene-like species. The decomposed products are oxidized to form another polymer film on the surface of an original DSmT film and a doping reaction observed earlier takes place on the composite polymer film. q1998 Elsevier Science S.A. All rights reserved.

Electrochemistry of poly[(tetraethyldisilanylene)quinque(2,5-thienylene)] (DSST) has been investigated in acetonitrile with cyclic voltammetry, potentiostatic oxidation and spectroelectrochemical measurements. In multicycle voltammograms of a DS5T film there are a pair of redox peaks attributable to anion-doping and dedoping. During potential cycling or electrolyzing at certain positive potentials, the polymer is subject to decomposition to some extent. An irreversible oxidation subpeak for the decomposition of the polymer is observed in the first-cycle voltammogram with low scan rates. Spectroelectrochemical measurements demonstrate that the slow decomposition process tends to be inhibited by further oxidation of its decomposed product, followed by redepositing of a solid film onto the DS5T film. The further oxidation of the decomposed product also leads to some unexpected observations in the spectroelectrochemistry of DS5T. Moreover, if the forward potential scanning is returned at more positive potentials, two pairs of oxidation/reduction peaks occur in the cyclic voltammogram of DS5T and the polymer film becomes much more unstable at the potential of the second oxidation peak.

Electrochemistry of s-p-conjugated polymers, poly[(hexamethyltrisilanylene)oligo(2,5-thienylene)] has been investigated in acetonitrile by using cyclic voltammetric and spectroelectrochemical techniques. Cyclic voltammograms of these polymers films display generally two pairs of main redox peaks, indicating the doping and dedoping processes of the polymers. The electrochemical oxidation of the polymer films results in their partial decomposition, besides the doping, which is shown by electrochemical quartz crystal microbalance and spectroelectrochemical measurements. The decomposition products are characterized by UV-visible absorption spectroscopy, fluorescence spectroscopy, FT-IR, and GPC measurements. It is concluded that the decomposition originates mainly from electrochemical cleavage of silicon-silicon bonds in the polymer chains, and the electrochemical stability of the s-p-conjugated polymers may be improved by decreasing the oligosilanylene block size in the polymer chains.