Showing papers by "Hideki Shirakawa published in 1994"

Synthesis and properties of liquid crystalline polyacetylene derivatives

Abstract: We have synthesized mono-substituted acetylenes with a liquid crystalline group and then poylmerized them with Ziegler-Natta and metathesis catalyts. The liquid crystalline group in the side chain of the polymer is composed of a cyclohexylphenoxy (PCH) or biphenoxy (BP) moiety as a mesogenic core, a methylene chain [-(CH 2 ) 3 -] as a spacer, and an alkyl chain as a terminal group. The polymers are abbreviated as PPCHn03A (n = 2, 3, 5 ∼ 8) or PBP503A. All polymers exhibited a fan-shaped texture in the polarizing microscope that is characteristic to smectic liquid crystalline phase, consistent with DSC measurements. Spectroscopic characterizations were carried out by means of IR, UV-VIS, 1 H- and 13 C-NMR, as well as evaluations of molecular weights by GPC and electrical conductivities upon iodine doping before and after magnetically forced alignment.

Electrochearcal synthesis of carbyne catalyzed by nickel complex

Abstract: Diiodoacetylene was electrolyzed at −2.0 V (vs. SCE) with a platinum cathode in dimethyl formamide containing a supporting electrolyte in the presence of a nickel complex, giving an insoluble black powder. Infrared spectrum of this product was similar to those of carbyne (polyyne) reported previously. A broad absorption at 2100 cm−1 due to a polyyne structure and broad absorptions ranged from 1700 to 1000 cm−1 due to a mixed structure of carbon-carbon double bond and other bonds were observed. The absorption at 2100 cm−1 reduced on a heat treatment under anaerobic conditions or on exposure to air. The electrical conductivity of pellet samples prepared from the black powder under a pressure of 600 kgf cm−2 was about 3 × 10−5 S cm−1.

Synthesis and characterization of highly conducting polyacetylene

Abstract: Polyacetylene can be synthesized by several routes. Among them, the most widely used method is an interfacial polymerization of acetylene monomer on a surface of a concentrated homogeneous Ziegler-Natta catalyst solution. The product is obtained as a form of thin films, which are served as specimens for characterization and measurements of various properties. The quality of the films is dependent strongly on preparative method of the catalyst as well as the polymerization condition of acetylene because there is no way to process the film due to its insolubility and infusibility. Synthetic conditions of highly conducting polyacetylene films and their characterization are reviewed in terms of catalyst preparations and polymerization methods.

Synthesis and properties of polythiophene derivatives with liquid crystallne substituents

Abstract: Summary form only given. In order to develop novel liquid crystalline conductive polymers, we have synthesized thiophene derivatives with liquid crystal groups and polymerized them by chemical and electrochemical polymerizations. The liquid crystalline substituents introduced into the thiophene ring consist of a phenyloyclohexyl (PCH) mesogen, a methylene chain [-(CH/sub 2/)/sub 4/-] as a spacer, and n-pentyl or n-hexyl chain, and are abbreviated as PCH504 or PCH604. The brominated precursor of PCHS04, for instance, was synthesized by reacting (trans-4-n-pentylcyclohexyl)phenol (PCH500) with Br-(CH/sub 2/)/sub 4/-Br (dibromobutane) in KOH. The Grignard reagent of PCH504-Br was coupled with 3-bromothiophene to obtain the PCH504-thiophene. The chemical and electrochemical oxidative polymerizations of the monomer gave insoluble powder of polymer. As a next step, the dehatogenative polycondensation of the 2,5 dibrominated monomer as well as the chemical oxidative polymerization of another kind of thiophene monomer that has no phenoxy-oxygen atom in the liquid crystalline substituent are underway.

Fused state/sup 13/C-NMR study on liquid crystalline polyacutylene derivatives - magnetically forced alignment and orientational behavior

Abstract: Summary form only given. Magnetically forced alignments and orientational behaviors of a series of side-chain liquid crystalline polymers, poly(mono-substituted acetylenes), as well as a liquid crystalline mononux, have been investigated through the fused-state/sup 13/C NMR measurements with proton dipolar decoupling. Upon a phase transition from isotropic to nematic or smectic phase, aromatic carbon signals notably shifted to the lower magnetic field, whereas aliphatic carbon signals slightly shifted to the higher magnetic field. This indicates that in the nematic or smectic phase, the side chain liquid crystal group is preferentially aligned along the direction of magnetic field. Analyses of chemical shift tensors are also carried out to evaluate an order parameter and shieldbig anisotropy in liquid crystalline phase, As a result, we have demonstrated that the liquid crystalline conjugated polymers are uniaxially aligned due to the magnetically forced alignment of the liquid crystalline side-chain, giving rise to a mono-domain structure.

A Novel Approach for Synthesis of Carbyne by Electroreductive Polymerization of Diiodoacetylene Catalyzed by Ni Complex

Abstract: Diiodoacetylene was electropolymerized with Pt cathode at −2.0 V (vs. SCE) in the presence of Ni complex in dimethylformamide (DMF) under anaerobic conditions, giving an insoluble black powder which had a strong infrared absorption at 2050 cm−1 and a broad Raman peak around 2150 cm−1 due to conjugated polyyne structure. A compressed pellet of the as-prepared sample had an electrical conductivity of 3 × 10−5 S cm−1.

Synthesis of liquid crystalline polyacetylene derivatives

Abstract: Mono-substituted acetylenes with liquid crystalline group consisting of phenylcyclohexyl and biphenyl moieties as mesogenic cores have been synthesized and polymerized using Ziegler-Natta and metathesis catalysts. Measurements of DSC and polarized microscopy showed that the polymers have smectic liquid crystal phases, while the monomer with phenylcyclohexyl moiety linked with octyl terminal group has nematic phase.

Positive-thermoelectric power of alkali-metal-doped polyacetylene

Abstract: The experimental results of electrical conductivity and thermoelectric power (TEP) of alkali-metal-doped polyacetylene are presented. The conductivities of (K0.14CH)x and (Rb0.17CH)x follow a power law of temperature. The temperature-independent conductivity anistroscopy ratios σ ∥ σ ⊥ for the stretch-oriented samples indicate a quasi-one dimensional charge transport characteristic in heavily doped polyacetylene. Also, we report the positve TEP of alkali-metal-doped polyacetylene. The temperature dependent TEP of K-doped polyacetylene is quasi-linear, which is characteristics to that of diffusive metals. Taking the slope of the linear temperature-dependent TEP, the density of states at the Fermi level for (K0.14CH)x is estimated to be η(RF)=0.19 states/eV C atom. The positive sign of TEPs for alkali-metal-doped polyacetylene can be understood by the quasi-one dimensional soliton condensed state model. The soliton band is nearly filled, which is possibly due to some compensation from impurities in doped polyacetylene, so that a hole-like charge transport can occur resulting in the positive TEP.

Polyacetylene films prepared by intrinsic non-solvent polymerization method - mechanical properties and electrical conductivities

Abstract: Summary form only given. We have synthesized highly stretchable and highly conducting polyacetylene films by Intrinsic Non-Solvent (INS) polymerization method and investigated the mechanical and electrical properties of the films, in order to examine the feasibility of the INS method as an advanced solvent-free polymerization method. The mechanical strengths of the films are 40 GPa in Young's modulus and 2.1 GPa in tensile strength. The electrical conductivities upon iodine doping are 2.2 - 4.3 x 10/sub 4/ S/cm, which are enhanced by 6 - 9 fold mechanical stretching. The results imply that the present films are more easily stretchable but less breakable than the films prepared by the solvent evacuation method (Young's modulus of 100 GPa and tensile strength of 0.9 GPa), leading to a remark that the INS method produces high quality polyacetylene films whose, mechanical and electrical properties are comparable and/or superior to those by the solvent evacuation method.

Unique electrical and optical properties of polyacetylene derivatives in liquid crystal phase

Abstract: Summary form only given. Polyacetylene derivatives substituted with long side chains containing mesogen unit such as poly[5-(p-(trans-4'-n-alkylcyclohexyl)phenoxy)-1-alkyne] exhibit unique liquid crystalline behavior. Dielectric constant of PPCH803A increases stepwise at the phase transition temperature between solid and liquid crystal phases, and the stepwise change is observed at the phase transition to liquid phase. Unique dependences of dielectric constant and optical transmission on the magnitude and frequency of applied voltage and magnetic field have been observed. The results are interpreted in terms of orientations of side chain of mesogen unit and also polymer main chain as functions of applied voltage and magnetic field.

Solid state properties and thermal isomerization behavior in polyacetylene films

Abstract: Summary form only given. Characterization of highly stretchable and highly conducting polyacetylene films synthesized by two kinds of solvent-free polymerization procedures, called Solvent Evacuation and Intrinsic Non-Solvent methods, have been performed with respect to the solid state properties and thermal isomerization behavior, by means of X-ray diffraction (XRD), scanning electron micrograph (SEM), and differential scanning calorimetry (DSC). We present here a deeper insight into the overall relationships between stretchability, crystallinity, and film thickness, and also a new aspect on the stepwise cis-trans isomerization mechanism. Morphological comparison has also been made by addressing traditional S-type polyacetylene films.

Side-chain liquid crystalline conjugated polymers, poly (mono-substituted acetylenes)

Abstract: Two kinds of mono-substituted acetylenes with liquid crystalline group consisting of phenylcyclohexyl and biphenyl moieties as mesogenic cores have been synthesized and polymerized by using Ziegler-Natta and metathesis catalysts. Measurements of DSC and polarized microscope showed that the polymers have smectic liquid crystal phases, while the monomer with phenylcyclohexyl moiety linked with octyl terminal group has nematic phase. Spectroscopic characterizations were made as well as evaluation of molecular weights and electrical conductivities upon iodine doping.

Syntheses of thiophene derivatives with liquid crystalline substituents and their polymerizations

Abstract: As a primary step to develop novel side-chain liquid crystalline conductive polythiophenes, we have synthesized a series of mono-substituted thiophene derivatives with phenylalkyl, phenoxyalkyl, and phenoxycyclohexyl group as a substituent and then polymerized them through chemical polymerization procedure. Characterizations of the thiophene monomers and polymers have been made from aspects of chemical and spectroscopic properties as well as molecular weights and electrical conductivity.

Liquid crystalline conducting polymers

Abstract: Recently we developed side chain liquid crystalline polyacetylene derivatives and achieved a substantial enhancement of electrical conductivity through magnetically forced alignment of the side chain of the polymer. When an electric field is employed as an alternative external force instead of the magnetic force, a ferroelectric liquid crystal should the more favorable than usual liquid crystals. This is because the former can respond more smoothly to the electric field owing to its spontaneous polarization than the latter. Here, in order to develop a novel liquid crystalline conducting polymer, we have synthesized a chiroptical liquid crystalline polyacetylene derivative. The liquid crystalline side chain of the polymer consists of a chiral alkyl moiety as a terminal group and a biphenyl moiety as a mesogenic core and a trimethylene segment as a spacer. The polymerization was carried out using a metathesis catalyst of MoCl{sub 5}-SnPh{sub 4}. Both the monomer and polymer showed the same signs in CD (circular dichroism) bands, indicating that the chirality of the monomer is maintained in the polymer. Measurements of DSC (differential scanning calorimeter) and polarizing microscope indicated that the polymer has a chiral smectic C (S{sub m} C*) phase assignable to the ferroelectric liquid crystal. Electrical and chemicalmore » properties of the polymer, including dielectric constant, electrical conductivity upon iodine doping and morphological alignment under an external force, are to be presented.« less