Lixiang Wang

Thermal behaviors of doped polyaniline

Abstract Thermal behavior of polyaniline (PAn) doped with kinds of inorganic or organic acids under desired atmosphere were studied by TG, DSC and in-situ electrical conductivity measurements. The reason for the thermal stability of electrical conductivity of doped PAn was discussed.

Structure and properties of self-doped polyaniline

Summary form only given. Sulfonated Polyaniline (SPAn) with various sulfonation degrees (SD) has been synthesized by the reaction of polyaniline and concentrated sulfuric acid using silver sulfate as catalyst. Only when SD of the SPAn is over 45% can it be dissolved in dilute aqueous alkaline solution and display apparent self-doping property. The reversible conversion between SPAn and its ammonium salt, confirmed by in-situ UV-Vis and ESR, is another evidence for the self-doping property of SPAn. From the different self-doping behavior of SPAn and poly (o-aminobenzoic acid), it is concluded that the formation of relatively strong intra-molecular ionic bonds is responsible for the effective self-doping property. 4-Amino-2-sulfonic acid diphenylamine is synthesized through Ullmann condensation, and successfully electropolymerized in H/sub 2/O/CH/sub 3/ CN/Na/sub 2/SO/sub 4/ system. The resulted polymer is a typical alternative compolymer of aniline and m-amino-benzenesulfonic acid. The differences in FTIR spectra and cyclic voltamograms between SPAn and the above alternative copolymer indicate that the sulfonic acid groups are somewhat randomly distributed on the backbone aromatic rings.

Thermal behavior of intrinsic polyaniline and its derivatrives

Abstract Thermal properties of polyaniline (PAn), polytoluidine (POT) and polyanisidine (PAs) were examined by TG and DSC techniques. The weight—uptake of POT at 200–300°C was observed and carefully discussed.

On the iodine-doping of polyaniline and poly-ortho-methylaniline

The reactions of polyaniline and poly-omicron-methylaniline of different oxidation degrees with I2 were followed by FTIR and electrical conductivity measurements. The results showed that the reaction of common polyanilines with I2 was oxidation in nature whereas that of the fully reduced ones was doping. The latter took place in two steps: oxidation of benzene-diamine units into quinone-diimine units (redox between I2 and the polymer chain) and formation of a conjugated system consisting of four aromatic rings (intramolecular chain redox).

Polytoluidines with different degrees of oxidation and their doping with HCl

Abstract Soluble polytoluidine was reacted with phenylhydrazine and iodine to obtain polytoluidines with different degrees of oxidation. Their reactions with HCl were followed by i.r. spectroscopy. Based on their spectral changes, a doping mechanism was proposed.

Synthesis and properties of poly (aniline-co-anisidine)

Summary form only given. Aniline and o-anisidine are chemically copolymerized at various temperature and monomer composition. Copolymerization reaction is confirmed by the solubility and electrochemical cyclic voltamograms of the resulted polymer. The pure copolymer can be separated from the homopolymers by THF/CHCl/sub 3/ two-step dissolution based on their solubility difference. O-Anisidine is more effective than o-toluidine to improve the solubility of Polyaniline. When the molar fraction of o-anisidine in monomer feed (f/sub 1/) is around 0.15-0.20, the resulted polymer is 100% soluble in THF, the corresponding tensile strength is more than 30 MPa and electrical conductivity remains at the magnitude of 10/spl deg/S/cm. When aniline and o-anisidine are copolymerized at low temperature (-5/spl deg/C), the resulted polymer is 100% soluble in THF, the tensile strength is more than 50MPa when f/sub 1/ is between 0.20-0.30 and its solution cast film shows apparent tensile yielding. GPC results demonstrate that the good solubility of the copolymer is related mainly to the steric repulsion between the methoxy groups. IR, /sup 13/C-NMR and F/sub 1/-f/sub 1/ (F/sub 1/ is molar fraction of anisidine in the copolymer) relationship indicate a random chain structure in the copolymer.

Polyaniline electrolytic capacitor

Aluminum solid electrolytic capacitors with polyaniline doped with inorganic and organic acids as counterelectrode were fabricated, their properties were studied.

Synthesis and characterization of chlorinated polyaniline

Summary form only given. Chlorinated polyaniline (Cl-PAn) with different Cl content has been synthesized in aqueous HCl/(NH/sub 4/)/sub 2/S/sub 2/O/sub 8/ system. The chlorination degree depends on aqueous HCl concentration in the reaction medium. The optimum condition to prepare Cl-PAn with high solubility and electrical conductivity is 6. 6 N HCl, equivalent monomer and oxidant concentration and at room temperature. This kind of Cl-PAn is 100% soluble in THF both in undoped and doped state, and its electrical conductivity is around 10/sup -4/S/cm. GPC result indicates that it has low number average molecular weight (Mn = 3523) and narrow molecular weight distribution (Mw/Mn = 2.14). Elemental analysis, FTIR, UV-Vis spectra and cyclic voltamograms of Cl-PAn are similar to those of poly (o-chloroanitine), indicating that Cl-PAn has similar structure as poly(o-chloroaniline). GC-MS and FTIR spectra demonstrate that chlorination happens at first on the monomer, then the chlorinated aniline homopolymerizes or copolymerizes with aniline. Once HCl concentration is over 7N, bi- or tri- chlorine substituted aniline can be formed, leading to great decrease in polymer yield and electrical conductivity.

LIGHT-ASSISTED OXIDATIVE DOPING OF POLYANILINES

Abstract A novel doping phenomenon of fully reduced polyaniline and poly-o-methylaniline, “light-assisted oxidative doping”, was found for the forst time. The doping reaction was followed by FTIR, UV-VIS, ESR and electrical conductivity measurements. It was shown that the fully reduced polyanilines in the form of HCl-salts undergo a spontaneous transition from an insulator or semiconductor to a conductor when exposed to air and light, and their final molecular chain structures are analogous to those found in HCl-doped common polyanilines.

Thermal behavior of doped polyaniline

Summary form only given. Thermal stability in air of polyaniline (PAn) doped with different dopant has been investigated by TG, DSC and in-situ electrical conductivity measurements. The onset temperature of apparent dopant evolution (Tc) for doped-PAn varies greatly from dopant to dopant. H/sub 2/SO/sub 4/- doped PAn is still stable at 190/spl deg/C whereas HCl evolves at 150/spl deg/C for the HCl-doped PAn. Electrical conductivity of sulfonated polyaniline keeps unchanged after it is treated at 200/spl deg/C for 2hr, but decreases 3-4 orders of magnitude after it is treated at 220/spl deg/C for 3hr. Thermal stability of PAn doped with organic acid such as (p-toluene sulfonic acid (TSA) , naphthalene 1,5-disulfonic acid or 5-sulphosaIicylic acid) is better than that doped with inorganic acids. The electrical conductivity of TSA-doped PAn decreases 4 orders of magnitude after it is treated at 230/spl deg/C for 2hr, but the IR and elemental analysis indicate that there is no dopant evolution during thermal treatment. The serious thermal oxidative cross-linking between PAn molecular chains at 220-250/spl deg/C is responsible for the decrease in electrical conductivity. Thermal stability of PAn doped with macromolecular acid (sulfonated polystyrene and sulfonated poly-p-phenylene oxide) is better than that of low molecular acid doped PAn.