Crystalline phases of electrically conductive poly(p-phenylene vinylene)

Poly(p-phenylene vinylene) (PPV) undergoes a first-order crystal-crystal phase transition when chemically doped with AsF₅, SbF₅, or H₂SO₄ or electrochemically oxidized with ClO^-₄ as the counterion. These structures have been observed using wide-angle x-ray diffraction. Doping with these agents does not disrupt the original orientation of the PPV crystallites. The crystalline phases obtained with all dopants employed here are similar in character, indicating a closely related family of electrically conductive structures having orthorhombic symmetry. An electrically conductive phase consisting of layers of polymer chains separated by a layer of the chemical dopant is proposed.     

One-step electrochemical synthesis of pure poly(2,5-dicyano-p-phenylenevinylene) films

In this communication we describe the electrochemical synthesis of poly(2,5-dicyano-p-phenylenevinylene) (DCNPPV) polymer films on indium tin oxide substrates. We investigate the purity, morphology, absorption and emission properties of the film. The purity was checked by infrared spectroscopy. The film formed presented spectroscopic purity equivalent to the chemically prepared PPV that was dialyzed for one week. Scanning electron microscopy of the surface revealed a grain-like morphology. The absorption and emission spectra showed absorption and emission bands at 420 nm and 575 nm, respectively, with the absorption onset at 422 nm, which corresponds to an energy gap of 2.25 eV. The electrochemical determination of the energy gap gives 2.05 eV, thus quite close to the optical energy gap at the onset of absorption. The EA and IP were determined by electrochemical measurements and are 3.46 eV and 5.51 eV, respectively.

An electrically conductive plastic composite derived from polypyrrole and poly(vinyl chloride)

An electrically conductive plastic material was obtained by the electrochemical polymerization of pyrrole in a poly(vinyl chloride) matrix. The transmission electron microscopy shows that polypyrrole is uniformly distributed in the matrix. The conductivity of the composites fall in the range of 5 to 50 S/cm, and their mechanical properties, as measured in a stress—strain test, are very similar to those of pure poly(vinyl chloride). These can be further improved by addition of poly(chloroprene) rubber as a plasticizer.     

Preparation and characterization of electrically conducting Langmuir-Blodgett films of poly(N-octadecylaniline)

A stable monolayer of N-octadecylaniline containing stearic acid at the air-water interface has been obtained. However, the Langmuir monolayer of pure poly(N-octadecylaniline) was not stable, but mixed Langmuir-Blodgett films of this polymer with stearic acid in different ratios as a spreading aid were stable. The electrical conductivity of these films increased by five orders of magnitude after doping with iodine as compared to that before iodine doping (5.8x10(-7) S cm(-1)). Temperature-dependent electrical conductivity suggested that these films were semiconducting in nature with low thermal activation energy. Impedance analyses of these films revealed that the equivalent circuit for poly(N-octadecylaniline) was (RQ) whereas that for mixed poly(N-octadecylaniline) with stearic acid was (RQ)(RQ).     

Gel processing of electrically conductive blends of poly(3-octylthiophene) and ultrahigh molecular weight polyethylene

The mechanical and electrical properties of solution-processed [or gel-spun] blends of poly(3-octylthiophene) and ultrahigh molecular weight polyethylene are discussed. Tensile drawing at elevated temperatures of the phase-separated blends resulted in significant improvements of the mechanical properties, in comparison with those of the neat conducting polymer, with values of the Young's modulus reaching > 40 GPa and tensile strengths in excess of 2 GPa. Doping of the undrawn polyblend fibers with iodine vapor or FeCl₃ resulted in materials of useful levels of electrical conductivity covering the full range of 10^?15 to 10 S/cm. A distinct percolation threshold for electrical conductivity was not observed, even at poly(3-octylthiophene) concentrations as low as 0.5 w/w %; the electrical conductivity of the latter blend, after doping with iodine vapor, was 8 × 10^?8 S/cm.     

Thermal transporting properties of electrically conductive polyaniline films as organic thermoelectric materials

Thermal transporting properties of electrically conductive polyaniline films were first investigated in wide range of temperatures above room temperature as organic thermoelectric materials. Thermal conductivities of various protonic acid-doped polyaniline films were measured by combination of a laser flash method and a differential scanning calorimeter in relation with electrical conductivity and a kind of dopant. The thermal conductivities thus measured are in the range of conventional organic polymers, indicating that the doped polyaniline films have extremely low thermal conductivities among electrically conductive materials, and have correlation with neither electrical conductivity, nor a kind of dopant. Consequently the polyaniline film, which shows very high electrical conductivity, has comparable thermoelectric figure-of-merit (ZT) with feasible inorganic thermoelectric materials such as iron silicide. This revised version was published online in August 2006 with corrections to the Cover Date.     

Morphological effect on spectral property of poly(9,9-dihexylfluorene-alt-2,5-dihexyloxybenzene) films

In this study the optical property and film morphology of a conjugated polymer, poly(9,9-dihexylfluorene-alt-2,5-dihexyloxybenzene) (PF6OC6), are investigated. It is found that the intensity of the 0-1 emission relative to the 0-0 emission in the PL spectra and the full width at the half-maximum (fwhm) of PL spectra of the PF6OC6 films decrease firstly and then increase with increasing the annealing temperature. The polymer films also exhibit different morphological features after annealing at different temperatures. The optical and morphological results suggest that the vibronic structure of PF6OC6 is closely related to the film morphology, and its formation is enhanced in the amorphous (or less ordered) films and inhibited in the ordered films.     

Regiodefined substituted poly(2,5-thienylene)s

The polymerization of 3,3″-dialkylterthiophenes overcomes the lack of regiospecificity associated (to some extent) with all the polymerization methods in use, thus allowing the preparation of perfectly regioregular polymers endowed with enhanced electrical and optical properties. Moreover, the larger spacing of the alkyl chains achieved with the insertion of an unsubstituted thiophene unit confers to such regioregular polymers an extraordinary doping stability. Two regiochemically defined alkoxy-substituted terthiophenes were also polymerized and the effects of the effects of the presence and position of the alkoxy group on the polymerization reaction and on the polymer properties are discussed. © 1993 John Wiley & Sons, Inc.     

NMR study of doped poly(2,5-dimethylaniline)

Structure changes and charge transfer in the doping process of poly(2,5-dimethylaniline) (PDMA) were studied by NMR technique. It was shown that not only the polymer chain but also the hydrogen atoms and methyl groups on the aromatic rings were involved in the charge transfer process. A “four ring BQ derivatives” model was proposed to explain the NMR results.     

Structure and properties of poly(2,5-dimethylterephthalamides)

Six methyl-substituted wholly aromatic polyamides were synthesized from the reaction of 2,5-dimethylterephthaloyl chloride with p-phenylenediamine, its 2,5-dimethyl and 2-methyl derivatives, m-phenylenediamine, or its 2-methyl and 4-methyl derivatives by solution polycondensation at low temperature. The x-ray diffraction diagrams of the polyamides obtained exhibit crystal patterns. Density values range from 1.26 to 1.37 g/cm³. NMR spectra determined in concentrated H₂SO₄ solution are reported. Poly(2,5-dimethylterephthalamides) have lower thermal stability than the corresponding polyterephthalamides. The increase in solubility of polyamide by the introduction of the 2,5-dimethylterephthaloyl linkage is accompanied by a decrease in thermal stability. The effect of methyl substituents on thermal properties and solubility is discussed in terms of the packing of polymeric molecules and the extent of hydrogen bonding of the amide groups.     

Multifunctional poly(2,5‐benzimidazole)/carbon nanotube composite films

The AB‐monomer, 3,4‐diaminobenzoic acid dihydrochloride, was recrystallized from an aqueous hydrochloric acid solution and used to synthesize high‐molecular‐weight poly(2,5‐benzimidazole) (ABPBI). ABPBI/carbon nanotube (CNT) composites were prepared via in situ polymerization of the AB‐monomer in the presence of single‐walled carbon nanotube (SWCNT) or multiwalled carbon nanotube (MWCNT) in a mildly acidic polyphosphoric acid. The ABPBI/SWCNT and ABPBI/MWCNT composites displayed good solubility in methanesulfonic acid and thus, uniform films could be cast. The morphology of these composite films was studied by X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The results showed that both types of CNTs were uniformly dispersed into the ABPBI matrix. Tensile properties of the composite films were significantly improved when compared with ABPBI, and their toughness (～200 MPa) was close to the nature's toughest spider silk (～215 MPa). The electrical conductivities of ABPBI/SWCNT and ABPBI/MWCNT composite films were 9.10 × 10^?5 and 2.53 × 10^?1 S/cm, respectively, whereas that of ABPBI film was 4.81 × 10^?6 S/cm. These values are ～19 and 52,700 times enhanced by the presence of SWCNT and MWCNT, respectively. Finally, without acid impregnation, the ABPBI film was nonconducting while the SWCNT‐ and MWCNT‐based composites were proton conducting with maximum conductivities of 0.018 and 0.017 S/cm, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1067–1078, 2010     

Ion conductive poly(ethylene oxide-dimethyl siloxane) copolymers

A series of poly(ethylene oxide-dimethyl siloxane) copolymers, — [SiMe₂O(CH₂CH₂O)_n]_m — (n = 2, 3, 4, 5, 6.4, 8.7, 13.3), were synthesised by the reaction of polyethylene glycol with dimethyl dimethoxy/diethoxysilane. Corresponding ion-conductive polymers were prepared by complexing these copolymers with salts (sodium tetrafluoroborate or ammonium adipate). The highest conductivity of these systems at room temperature was 3 × 10⁻⁴ S cm⁻¹ and 6 × 10⁻⁵ S cm⁻¹, respectively. The glass transition temperature of these copolymers is reported and is seen to be dependent on the length of the ether units. The effects of siloxane content, salt concentration, and temperature on the conductivity are discussed. © 1996 John Wiley & Sons, Inc.     

Reliability of flexible electrically conductive adhesives

Based on our previous work about electrically conductive adhesives (ECAs), a flexibilizer named 1,3‐propanediol bis (4‐aminobenzoate) was used to fabricate flexible ECAs (FECAs). ECAs, FECAs, and electronic devices connected by them were carried out the hot and humid aging test under constant humidity level of 85% relative humidity at 85 °C for 600 h. After aging, the bulk resistance change of ECAs was about 26%, that of FECAs was a little higher, about 29%. The contact resistance change of devices connected by ECAs and FECAs was very great, about 450% and 410%, respectively. The bonding area at connection interface between colloids and devices had delamination, even cracks. The delamination of ECAs was calculated about 60%, the average shear strength of ECAs was reduced about 45%, and those of FECAs were about 50% and 30%, respectively, so FECAs had a higher bonding stability in hot and humid environment. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and electrical conductivity of poly(arylene vinylene). I. Poly(2,5-dimethoxyphenylene vinylene) and poly(2,5-dimethylphenylene vinylene)

The highly conjugated aromatic polymers, poly(2,5-dimethoxyphenylene vinylene) and poly(2,5-dimethylphenylene vinylene), were obtained from their water soluble, sulfonium salt precursor polymers. Films of these polymers were reacted with either AsF₅ or I₂ vapor. Poly(2,5-dimethoxyphenylene vinylene) showed increases in electrical conductivity of up to 14 to 15 orders of magnitude for these two dopants, while an 8 to 9 order of magnitude increase was observed for poly(2,5-dimethylphenylene vinylene) with the same dopants. The synthesis of the precursor polymers, the properties and elimination reactions of films of the precursors, the doping reactions, and the conductivities of the resulting phenylene vinylene films are discussed.     

Photochemical behavior of poly(ethylacryloylacetate) and poly(acryloylacetone) films

Films of poly(ethylacryloylacetate) (PEAA) and poly(acryloylacetone) (PAA) were subjected to UV irradiation (λ = 254 nm) at room temperature. The photoinduced structure transfer from cis-enol onto a diketo forms has been investigated. The structure transfer caused by UV light was found to be slower than for the corresponding process in solution. The spectral investigations (UV, IR) showed reversible process of photoketonization. The results were analyzed in terms of the model for the participation of the trans-enol form in the process of the ketonization. Based on the results obtained, some general conclusions were made about the organization of the units in the polymer chain. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3683–3688, 1997     

Highly conductive meta derivatives of poly(phenylene sulfide)

Changes in the backbone structure of several meta derivatives of polyphenylene sulfide upon doping with AsF₅ have been investigated by IR spectroscopy. Poly(m-phenylene sulfide) does not form a conducting complex with AsF₅ unless reacted under conditions where carbon-carbon bonds form intramolecularly between phenyl rings. This assertion has been verified by comparison of the IR spectra of poly(m-phenylene sulfide) and a newly synthesized derivative, poly(thio-3,7-dibenzothiophendiyl), after doping with AsF₅. This new derivative forms a complex with AsF₅ which exhibits a conductivity of 18.5 S/cm. A sulfone-containing derivative has also been synthesized, poly[thio-3,7-(dibenzothiophene-5,5-dioxide)-diyl]. With this polymer, a much lower conductivity, 10^?3 S/cm, was obtained after exposure to AsF₅.