Susumu Tanaka

Electrochemical preparation of conducting poly(3-methylthiophene): comparison with polythiophene and poly(3-ethylthiophene)

Optimal conditions for the electrochemical polymerization of 3-methylthiophene were studied. A good solvent and electrolyte were propylene carbonate (PC) and tetraethylammonium hexafluorophosphate (Et4NPF6), respectively. The effects of preparation conditions were also examined using this solvent and electrolyte. Electrical and other properties of poly(3-methylthiophene) (PMT) were compared with those of polythiophene (PT) and poly(3-ethylthiophene) (PET) prepared under the same polymerization conditions. The conductivity increased in the order PT<PET<PMT. The infrared spectra of these polymers indicated that an observable number of bondings other than 2,5 linkages are present in PT, but not in PMT or PET. Cyclic voltammograms suggested the oxidation potential to increase in the order PMT<PET<PT. Changes in visible-near infrared spectra during electrochemical doping were measured. In neutral states, band gaps increased in the order PMT<PT<PET. At intermediate stages of doping, two peaks appeared in the band gap region. At the most advanced stages, a broad peak remained. PMT showed a frequency dependence of spectral change similar to that of PET. These results are discussed in terms of the steric and electronic effects of the substituents and their compatibility with bipolaron theory.

Soluble conducting polymers by electrochemical polymerization of thiophenes having long alkyl substituents

Abstract Poly(3-hexylthiophene) (PHT), poly(3-octylthiophene) (POT), poly(3-dodecylthiophene) (PDDT), poly(3-octadecylthiophene) (PODT) and poly(3-eicosylthiophene) (PEIT) were electrochemically prepared. Their conductivities were 95-11 S/cm. Neutral PHT, POT and PDDT were soluble in chloroform, their degrees of polymerization being 2.3 × 102, 1.4 × 102 and 9 × 10, respectively. An as-grown film and the films cast from the oxidized and neutral PDDT solution in chloroform were found to be electrochemically active. Visible-near infrared spectra of the PDDT film as a function of oxidation potential resembled those of poly(3-methylthiophene) and poly(3-ethylthiophene). The oxidized PDDT in chloroform solution showed absorption spectra suggesting the existence of bipolarons.

Soluble conducting polythiophenes

Tractable polythiophenes which are soluble in ordinary organic solvents at ambient temperatures are prepared by the electrochemical polymerization of thiophenes having a long alkyl chain.

Electrochemical preparation and properties of poly(3-methoxy-2,5-thiophenediyl) and poly(3-methylthio-2,5-thiophenediyl)

Abstract Soluble and conductive poly(3-methylthio-2,5-thiophenediyl) and poly(3-methoxy-2,5-thiophenediyl) films were prepared by the electrochemical polymerization of 3-(methylthio)thiophene (MTT) and 3-methoxy-thiophene (MOT), respectively. The polymers were identified from their i.r. spectra and found to be soluble in chloroform, propylene carbonate (PC), dimethyl sulfoxide (DMSO) and 1-methyl-2-pyrrolidinone (NMP). When doped, they were soluble in PC, DMSO and NMP. Cast films could be obtained from their solutions. The degrees of polymerization of poly-MTT and poly-MOT were 7.4 and 79, respectively. The vis-near i.r. specta of either polymer solution had characteristic peaks due to bipolarons. The doped poly-MTT solution became undoped after four days in air. The doped poly-MOT solution was stable for a few months, and the conductivity of the pressed pellet of doped poly-MOT did not change for as long as 11 months. With regard to differences in the absorption spectra between the films and solutions of the undoped state, the films had bands at longer wave-length than the solutions. The shifts may possibly have been due to internal rotation about single bonds, probably occurring more freely in solution than in films. Solid-state samples retained the coplanar configuration. In cyclic voltammograms, the oxidation potential of poly-MOT was lower than 0 V versus Ag/Ag+. It is thus evident that the doped state of poly-MOT is stable in air.

Electrochemical preparation of conducting polyalkylthiophene films

Abstract Polythiophene (PT), poly(3-methylthiophene) (PMT), poly(3-ethylthiophene) (PET), Poly(3-butylthiophene) (PBUT) and poly(3-benzylthiophene) (PBZT) were prepared electrochemically under the same polymerization conditions. Their properties were compared by conductivity measurement, Fourier transform i.r. spectrometry, cyclic voltammetry and visible-near i.r. spectrometry during electrochemical doping. PMT and PET showed higher conductivity than PT. Electron-donating effects of alkyl groups lowered the oxidation potential and stabilized anion-doped states. In neutral states, band gaps increased in the order PMT

Structure and properties of polythiophene derivatives

Abstract Soluble and conducting poly(3-methoxythiophene) (poly-MOT) and poly(3-methylthiothiophene) (poly-MTT) films were prepared by the electrochemical polymerization of the corresponding monomers. The doped polymers were soluble in propylene carbonate (PC), dimethyl sulfoxide (DMSO), and 1-methyl-2-pyrrolidinone (NMP). Cast films could be obtained from their solutions. The degrees of polymerization of poly-MOT and poly-MTT were 79 and 7.4, respectively. The visible-near i.r. spectra of either polymer solution had characteristic peaks due to bipolarons. The doped poly-MOT was stable in air, due to its low oxidation potential. Poly-MOT was also prepared by the oxidative coupling of MOT with FeCl 3 . The conductivity of a poly(3-phenylthiophene) (poly-PT) film was 140 S/cm. Its cyclic voltammograms showed well-defined waves corresponding to cation-doping as well as anion-doping. Spectral changes during electrochemical reduction indicate that cation-doping really took place. At low levels of anion-doping, an unambiguous peak associated with transition between two polaron bands was observed. Poly(3-methylpyrrole) (poly-MPY) films were electrochemically prepared and their properties were compared with those of polypyrrole (poly-PY). The condutivity of a poly-MPY film was 220 S/cm, two orders of magnitude higher than the reported value, and its oxidation potential was lower than poly-PY, suggesting that polypyrroles having higher alkyl groups might be soluble conducting polymers and stable in doped states.

Preparation of poly(3-octylpyrrole) by oxidative coupling

Abstract N -Tolylsulfonylpyrrole was allowed to react with octanoyl chloride in the presence of tin(IV) chloride to give octanoyl- N -tolylsulfonylpyrrole, which was hydrolyzed with sodium hydroxide and reduced with lithium aluminum hydride to give 3-octylpyrrole (OCPY). Poly(3-octylpyrrole) (POCPY) was prepared by the oxidative coupling with copper(II) and iron(III) perchlorates. The conductivity of pressed pellets was 1.6 S cm −1 . The infrared spectrum was similar in the out-of-plane deformation region of pyrrole rings to that of an electrochemically polymerized film. Doped POCPY was soluble in organic solvents and its solution spectra had two peaks, their positions being dependent on the solvents used for the measurement. The spectra changed greatly in N -methylpyrrolidinone under vacuum in 9 days, but showed that POCPY was still in a doped state in isobutyl methyl ketone after 28 days. The spectrum of a film cast from the pyridine solution had two peaks at the same positions as those of the original solution, but indicated partial undoping had taken place.

Electrochemical preparation of highly conducting polythiophene films

Electrochemical polymerization of thiophene, 3-methylthiophene, and 3-ethylthiophene in propylene carbonate gave tough films, having conductivities of 190, 510, and 270 S cm–1, respectively.

Electrochemical polymerization of dithienylbenzene and dithienylpyridine

Abstract 1,4-Bis(2-thienyl)benzene (T14B), 2,5-bis(2-thienyl)pyridine (T25P), and 2,6-bis(2-thienyl)pyridine (T26P) were electrochemically polymerized. The conductivity of poly-T14B, poly-T25P, and poly-T26P was 1.7 × 10−1, 2.6 × 10−8, and 1.2 × 10−7 S/cm, respectively. A poly-T26P film has a very even surface and is composed of fibrils growing on a thin, dense layer. Infrared spectra showed the monomer units to be linked through the 5,5′-positions of the thiophene rings. On electrochemical oxidation, poly-T26P became a quaternary ammonium salt. Visible/near-infrared spectra of poly-T14B showed that bipolaron states were formed. The conductivities of poly-T25P and poly-T26P rose to about 10−2 S/cm by iodine doping, irrespective of the bonding sites of pyridine.

Soluble conducting polypyrrole: poly(3-octylpyrrole)

Electrochemical polymerization and oxidative coupling of 3-octylpyrrole yielded a soluble and conducting polymer which showed characteristics different from poly(3-alkylthiophenes) and poly(3-methoxythiophene).