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.

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.

UV-visible absorption and fluorescence properties of three series of s-pconjugated polymers (copolymers of alternative oligothienylene and oligosilylene units) have been studied in dioxane solution. The energies of the absorption maximum, fluorescence maximum, and the 0-0 transition are found to be linearly dependent on the reciprocal of the number of thiophene rings in the repeating unit of the polymer chain, but almost independent of the silicon atom number. The s-p-conjugation in the polymers results in red shift in the absorption and fluorescence maxima, higher fluorescence quantum yields, and longer fluorescence lifetimes of the polymers, with respect to their corresponding analogous a-oligothiophenes.

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.

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.