Ichiki Murase

Highly conducting poly(phenylene vinylene) derivatives via soluble precursor process

Abstract Highly stretched PPV films were successfully prepared via pyrolysis of a soluble precursor polymer of sulfonium salt with stretched ratio of 10 to 15. The conductivity reached to 4 −5×103 S/cm by H2SO4 doping. The dichroism in polarized ir spectra was found to be the optimum measure for the degree of orientation of the PPV film. The conductivity increment of stretched PPV film doped with H2SO4 was also found to have a good relation to the dichroic ratio of the phenyl group at 1520cm−1. PPV films with dimethoxy- and diethoxy substituents at 2,5-position were prepared by the sulfonium salt process for the first time. By I2 doping, these films showed high conductivity of over 200 S/cm which is far from 10−3 S/cm of non-substituted PPV. Molecular orbital calculations suggest that the introduction of the alkoxy group lowers the ionization potential of PPV and enhances the affinity of PPV to an acceptor dopant.

Highly conductive graphite film prepared from pyrolysis of poly(p-phenylene vinylene)

Pyrolysis of poly(p-phenylene vinylene), PPV, up to 3000 °C was studied in relation to the molecular orientation in the PPV film prepared via decomposition of a soluble precursor sulphonium salt polymer and simultaneous biaxial stretching. The conductivity of PPV pyrolysed at 3000 °C was strongly influenced by biaxial stretching and reached 104 S/cm as it was and 105 S/cm by SO3 doping at three-fold stretching, while conductivities of non-stretched PPV were 103 S/cm and 104 S/cm, respectively. The conductivity obtained for the stretched PPV is comparable to that of a highly oriented pyrolytic graphite (HOPG) or natural graphite. X-ray diffraction analyses for the stretched PPV and the pyrolysed products suggest that the biaxial stretching induces planer orientation in PPV and facilitates its graphitization. It is noteworthy that PPV film is pyrolysed to give a highly oriented graphite maintaining the film form. The Raman spectrum analysis indicated that the film is converted into a pure graphite above 2750 °C.

Highly Conducting Poly(P-Phenylene Vinylene) Prepared From Sulfonium Salt

Abstract Highly conducting poly(p-phenylene vinylene), PPV, has been obtained via pyrolysis of the soluble precursor polymer derived from p-xylylene bis(diethyl sulfonium bromide) which is processed to film. The highly oriented PPV film is obtained by stretching the precursor film up to ten fold at a higher temperature. The films show extremely high conductivity of 2780 S/cm and 491 S/cm by doping AsF 5and SO3 respectivly, with high electrical anisotropy.

Preparation of graphite film by pyrolysis of polymers

Abstract Pyrolysis of aromatic polymers up to 3000°C was studied in relation to the molecular structure and orientation. Poly(p-phenylene vinylene), PPV, was pyrolyzed to give highly oriented graphite in keeping film form. Raman spectrum analyses indicated that PPV was converted into pure graphite above 2750°C. The graphite film obtained showed 104 S/cm as it was and 105 S/cm by SO3-doping, which are comparable to those of the highly oriented pyrolytic graphite (HOPG). X-ray diffraction analyses and scanning electron micrographs for the pyrolyzed products suggest that the biaxial stretching facilitates graphitization of PPV and orientation of the graphite plane. Aromatic polyimide was also converted into graphite and showed 104 S/cm after pyrolysis at 3000°C, while aromatic polyamideimide and polyamide showed 103 S/cm at most after pyrolysis at the temperature.

Preparation and properties of highly conducting poly(arylene vinylenes)

Abstract Highly electroconductive poly(p-phenylene vinylene), PPV, films were successfully prepared by preventing a side reaction in pyrolysis of a soluble precursor polymer. The conductivity of PPV film reached 104 S/cm by H2SO4 doping because of decreasing sp3 defects. The number of conjugated units in the new PPV films was estimated to be about 103 from the molecular weight dependence of the conductivity. Other poly(arylene vinylenes) were indicated to have shorter conjugation length than PPV. PPV fibers were also prepared from the soluble precursor polymer by a dry-spinning method. The stretched fiber of PPV showed a high conductivity of 2.7×104 S/cm by H2SO4 doping and high tensile strength of 200 kg/mm2 as it was.

UV photoemission spectroscopy of poly(p-phenylene vinylene) (PPV)

Abstract UV photoemission spectra of poly(p-phenylene vinylene) were measured for films prepared by (i) vacuum evaporation and (ii) in-situ pyrolysis of precursor polymer. The results were analyzed using the theoretical band calculations, the data of other phenyl-containing polymers, and reported XPS spectrum. The effect of further heat-treatment of the PPV film was also examined.

UV PHOTOELECTRON-SPECTROSCOPY OF CONDUCTING POLYMERS AND THEIR MODEL COMPOUNDS

Abstract UV photoelectron spectra were measured of p-phenyls (as model compounds of poly(p-phenylene)), poly(p-phenylene sulfide), poly(p-phenylene vinylene), beta-carotene (as a model compound of polyacetylene), and poly(dimethylsilane). Accurate values of ionization threshold and width of the uppermost valence band were determined, and they are discussed in relation to acceptor doping and electrical conduction.

ESR and ENDOR study of poly (phenylene vinylene)

Abstract ESR and ENDOR measurements were performed on undoped poly (p-phenylene vinylene) films obtained by stretching the precursor films under inert gas atmosphere at temperatures between 100°C and 400°C. Weak ESR signals of the spin concentration being roughly 1 spin / 10 6 C 8 H 6 unit appeared as the temperature of preparation increased. g value was about 2.003. Spectra showed a clear anisotropy both in g value and line width, where both quantities are larger for the stretch direction. Proton ENDOR signals were also detected and showed larger coupling values for the stretch direction. Observed anisotropy of ESR and ENDOR is qualitatively similar as those observed in stretch oriented polyacetylene, suggesting that the unpaired electrons are π-electron defects on the conjugated molecular chain.