Poole-Frenkel effect in amorphous poly(p-phenylene sulfide)

The conductivity of poly(p-phenylene sulfide) (PPS) amorphous samples sandwiched between metallic electrodes has been studied as a function of applied voltage, temperature, and electrode material. The voltage (U) dependence of the currents for electric fields within the range 10³–10⁶ V/cm exhibits exp βU^1/2 behavior with β = β_Schottky below the glass transition temperature (T_g ≊ 90°C), and β = β_{Poole-Frenkel} above T_g. Coordinated temperature measurements of dc currents with different metallic contacts and thermally stimulated currents (TSC) indicate, however, that the conductivity at T < T_g is consistent with the so-called “anomalous” Poole-Frenkel effect rather than the Schottky effect. Consequently, the p-type conductivity in amorphous PPS is proposed to be a bulk-limited process due to ionization of two different types of acceptor centers in the presence of neutral hole traps. © 1996 John Wiley & Sons, Inc.     

Crystal structure of poly(p-phenylene) prepared by organometallic technique

The two-dimensional crystal structure of poly(p-phenylene) is investigated by linkedatom Rietveld analysis of the x-ray diffraction powder profile. Two molecular chains are packed in a rectangular pgg unit cell (a = 0.779 nm; b = 0.551 nm) with a paracrystalline shift distortion along the chain axis. The molecular conformation is not rigidly planar; rotations between adjacent phenyl-ring planes in a molecule alternate with an angle of about 20°. The setting angle between the mean molecular plane and the a axis is 55.5°.     

Electrochemical properties and photoelectrochemical response of vacuum-deposited poly(p-phenylene) thin films

The electrochemical properties of a poly(p-phenylene) (PPP) thin film prepared by vacuum deposition were investigated by cyclic voltammetry in organic and aqueous media with a lithium perchlorate electrolyte. The PPP thin film was able to undergo both n-doping and p-doping reversibly. In an aqueous medium, the cyclic voltammograms indicated the characteristic loop in a potential sweep. The loop was ascribed to the charge transfer on the PPP film surface and to an accumullation effect of the charge in the PPP film. A photocurrent was observed at the PPP film under UV light irradiation.     

Aggregation of sulfonated poly(p-phenylene terephthalamide) in dilute solutions

The viscosities of dilute solutions of poly(p-phenylene terephthalamide), PPTS, in dimethylacetamide, water, and their mixtures were determined. The reduced viscosity plot in dimethylacetamide shows a negative slope. When the water content in the mixed solvent in 90% or higher, there is an upswing in the reduced viscosity values at concentrations below 0.1 g/dL. The latter behavior suggests a “polyelectrolyte” effect. However, an association model was found to be able to explain the viscosity behaviors in both solvents. ©1995 John Wiley & Sons, Inc.     

Molecular dynamics simulations of a poly(p-phenylene) oligomer

We have studied the conformation and coefficient of thermal expansion in the poly(p-phenylene) oligomer p-sexiphenyl (C₃₆H₂₆) by molecular dynamics simulations. Studies of the backbone phenyl–phenyl torsion angle in a simulated p-sexiphenyl crystal at room temperature indicate the presence of torsional librations of approximately ±20°. Further analysis of the phenyl–phenyl backbone torsion angle in less closely packed regions of the simulated crystal (crystal ends) indicate the presence of 180° phenyl ring flips, in agreement with solid-state deuterium NMR data on poly(p-phenylene oligomers). The linear coefficient of thermal expansion was also calculated and found to be negative, in qualitative agreement with experimental data on rigid-rod compounds. © 1993 John Wiley & Sons, Inc.     

Effect of sizing materials of carbon fiber on solid-state cure of poly(p-phenylene sulfide)

The effect of sized carbon fibers on the solid-state cure of poly(p-phenylene sulfide) (PPS) was studied using differential scanning calorimetry. PPS resin reinforced with sized carbon fiber exhibited the largest cure peak for all cure temperatures and showed a second peak at low cure temperature which was absent in both PPS reinforced with desized carbon fiber and neat PPS resin. In a separate experiment in which epoxy prepolymer/PPS mixture was cured, the exothermic reaction was related to the presence of the epoxy sizing used on the carbon fiber. © 1998 John Wiley & Sons, Ltd.     

2H NMR characterization of phenylene ring flip motion in poly(p-phenylene vinylene) films

Solid-state ²H quadrupole echo nuclear magnetic resonance (NMR) spectra and measurements of ²H spin lattice relaxation times have been obtained for films of poly(p-phenylene vinylene) deuterated in phenylene ring positions (PPV-d₄). NMR line shapes show that all the phenylene rings of PPV undergo 180° rotational jumps about the 1,4 ring axis (“ring flips”) at 225°C. The temperature dependence of the ²H line shapes show that the jump motion is thermally activated, with a median activation energy, E_a = 15 kcal/mol, and a distribution of activation energies of less than ±2 kcal/mol. The jump rate was also determined from the magnitude of the anisotropic T₂ relaxation associated with ²H line shapes and from the curvature of inversion recovery intensity data. The experimental activation energy for jumps is comparable to the intramolecular potential barrier for rotation about phenylene vinylene bonds. ²H NMR provides a method for determining the phenylene-vinylene rotational barrier in pristine PPV, and may potentially be used to study conjugation in conducting films.     

Synthesis and Kerr effect of p-phenylene vinylene oligomers

The molecular dynamics of p-phenylene vinylene (PPV) oligomers, synthesised by a condensation reaction and separated by molecular distillation, have been investigated using the electrooptic Kerr effect. The experimental Kerr constants of these materials change sign from positive to negative in going from n = 1 to n = 2 and are not in good agreement with theoretical results. The discrepancies, which increase in magnitude as n increases, can be attributed to solvent-solute interactions, the nonplanar nature of PPV oligomers, or the nonvalidity of the additivity scheme chosen for calculation of theoretical quantities. © 1996 John Wiley & Sons, Inc.     

Synthesis and ionic conductivity of hyperbranched poly(glycidol)

A novel hyperbranched poly(glycidol) (HPG) was prepared and characterized. The synthesized HPG was used as a substrate of a polymer electrolyte. The ionic conductivity of a blend of HPG, polyurethane (PU), and salt was studied. The ionic conductivity of HPG/PU/LiClO₄ was about 6.6 × 10^?6 S · cm^?1 at 20 °C and 6.3 × 10^?4 S · cm^?1 at 60 °C. The results indicated that HPG showed higher solubility for salt than linear polyether when both had the same [O]/[Li⁺] molar ratio. The main reason was that more cavities and a lower degree of chain entanglement in HPG resulted in a lower glass‐transition temperature and were beneficial for decreasing the aggregation of salt or enhancing the ionic conductivity. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2225–2230, 2001     

高分子量PPV的合成、掺杂及导电性

高分子量的聚对苯乙炔（ＰＰＶ）是从单体１．４一二氯甲基苯合成,后者聚合产生水溶性铳盐,此时,对于ＰＰＶ的转换可用二甲硫醚和盐酸的热消除反应,从水溶液中成膜。用ＩＲ、ＵＶ－Ｖｉｓ、ＴＧＡ分析研究了消除反应。ＰＰＶ膜具有良好的机械性能,而且可能是由于ｎ－和ｐ－型杂质得到的材料具有的导电性近似于这些高掺杂聚乙炔。中间聚电解质的转换率对于ＰＰＶ可能是一种调整,并且这些掺杂膜的导电性,可能与平均共轭长度有关     

Effect of amorphous precipitated silica on the properties and structure of poly(p-phenylene sulfide)

Using a precipitation technique, silicas were obtained from sodium metasilicate solution employing an acidic agent. Alcohol solutions were used in the process of production of highly dispersed silicas, which resulted in partial blocking of the silica surface silanol groups. Moreover, studies on morphology and microstructure using transmission electron microscopy and scanning electron microscopy were performed. The size distributions of primary particles and aggregate and agglomerate structures were determined using a ZetaPlus instrument using the dynamic light scattering method. The structure and molecular dynamics of the nanocomposite, consisting of poly (p-phenylene sulfide) (PPS) and of the precipitated silica, were studied using atomic force microscopy and nuclear magnetic resonance. It was proved that during annealing the fragmentation of PPS agglomerates takes place. This phenomena probably resulted from repulsion forces existing between agglomerates and aggregates. Fragmentation in the polymer network probably resulted from repulsion forces between agglomerates and smaller aggregates. Received: 7 November 2000 Accepted: 5 April 2001     

Synthesis and Characterization of Poly(p-phenylene benzobisoxazole)/Poly(pyridobisimidazole) Block Copolymers

Poly(p-phenylene benzobisoxazole)/poly(pyridobisimidazole) block copolymers (PBO-b-PIPD) were prepared by introducing poly(pyridobisimidazole) (PIPD) moieties into the main chains of poly(p-phenylene benzobisoxazole) (PBO) in order to enhance its photostability. PBO and copolymer fibers were directly prepared from the polymerization solutions by dry-jet wet-spinning. Chemical structures and molecular chains arrangement of the block copolymers were characterized by Fourier transform infrared (FTIR) spectroscopy, solid-state ¹³C-NMR and wide angle X-ray diffraction (WAXD). Thermal stability of the copolymers was investigated by thermogravimetric analysis (TGA) in nitrogen. Thin films of PBO and copolymers were cast from methanesulfonic acid (MSA) solutions. Both the films and fibers were exposed to UV light to determine their photostability. Changes in the chemical structures and surface morphologies of the films were characterized by FTIR spectra and scanning electronic microscopy (SEM), respectively. After UV light exposure, the retention of strength for copolymer fibers is improved compared to PBO fibers. The results revealed that copolymers suffered less photodegradation in comparison with homopolymer. The mechanism for the improved photostability of the copolymers was discussed.     

Structure and property development in poly(p-phenylene terephthalamide) during heat treatment under tension

The evolution of several structural characteristics during isothermal heat treatment of poly(p-phenylene terephthalamide) was studied. In this work, heat treatment was interrupted after different treatment times, with the specimens immediately quenched to room temperature. These specimens were then characterized by tensile testing, wide- and small-angle x-ray scattering, and optical microscopy. Structural parameters obtained from these measurements relate to crystal perfection (via the paracrystalline axial distortion parameter), axial crystallite size, transverse crystallite size, degree of chain misorientation, and degree of pleating. Structural and mechanical parameters were then plotted against heat-treatment time to obtain kinetic isotherms for each parameter. The kinetics of the removal of chain misorientation parallels that of tensile modulus increase under all conditions. Of the other structural parameters, only the kinetics of pleat removal mimics that of modulus change, indicating that pleat removal is the effective cause of increased chain alignment and thereby of increased axial stiffness. ©1995 John Wiley & Sons, Inc.     

Head-to-tail regioregularity of poly(3-hexylthiophene) in oxidative coupling polymerization with FeCl3

We investigated a head-to-tail regioregularity of poly(3-alkylthiophenes) from 3-alkylthiophene by an oxidative coupling polymerization, which is the simplest and easiest way for the synthesis of polythiophenes. The polymerizations were conducted using ferric chloride (III) as an oxidant in chloroform. Investigating the polymerization conditions, a lower temperature and a lower concentration were effective for increasing the head-to-tail (HT) content. The best HT content of 88% was obtained when the temperature was −45°C and the initial monomer concentration was 0.02 mol L⁻¹. Washing the resulting polymer by n-hexane further increased the content to 91%. Thus, it was found that the high regioselectivity can be achieved by the simple polymerization and the simple operation such as washing. The polymerization mechanism causing the regularity is also discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1943–1948, 1999     

Synthesis of graft polymers with poly(isoprene) as main chain by living anionic polymerization mechanism

The graft polymers [poly(isoprene)‐graft‐poly(styrene)] (PI‐g‐PS), [poly(isoprene)‐graft‐poly(isoprene)] (PI‐g‐PI), [poly(isoprene)‐graft‐(poly(isoprene)‐block‐poly(styrene))] PI‐g‐(PI‐b‐PS), and [poly(isoprene)‐graft‐(poly(styrene)‐block‐poly(isoprene))] PI‐g‐(PS‐b‐PI) with PI as main chain were synthesized through living anionic polymerization (LAP) mechanism and the efficient coupling reaction. First, the PI was synthesized by LAP mechanism and epoxidized in H₂O₂/HCOOH system for epoxidized PI (EPI). Then, the graft polymers with controlled molecular weight of main chain and side chains, and grafting ratios were obtained by coupling reaction between PI^?Li⁺, PS^?Li⁺, PS‐b‐PI^?Li⁺, or PI‐b‐PS^?Li⁺ macroanions and the epoxide on EPI. The target polymers and all intermediates were well characterized by SEC,¹H NMR, as well as their thermal properties were also evaluated by DSC. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Coagulation of poly(p-phenylene benzobisoxazole) in polyphosphoric acid using aqueous and nonaqueous solutions

Diffusion of aqueous and nonaqueous coagulants into lyotropic/nematic solutions of poly(phenylene benzobisoxazole) in polyphosphoric acid using fluorescence microscopy is reported. The fluorescence microscopy technique offers advantages in that the experiment is independent of the coagulant and the experiments can be performed in a front surface mode so that optically thin samples are not required. The diffusion process is modeled as Case II diffusion as described by Crank and Park. The apparent diffusion coefficients are found to range from ～ 2 × 10^?6 cm²/s to ～ 2 × 10^?7 cm²/s for aqueous and nonaqueous coagulants. The apparent diffusion coefficients can be varied by several orders of magnitude (e.g., down to ～ 3 × 10^?10 cm²/s) by varying the concentration of polyphosphoric acid in the coagulant. © 1995 John Wiley & Sons, Inc.     

Enhancement of electroluminescence intensity in poly(3-alkylthiophene) with different alkyl side-chain length by doping of fluorescent dye

Electroluminescent diodes utilizing poly(3-alkylthiophene) (PAT) containing fluorescent dyes have been fabricated and their unique enhancement of emission characteristics have been studied. Remarkable enhancement of the electroluminescence efficiency has been observed for diodes with PAT doped with oxadiazole derivative (2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole; PBD) and perylene derivative (N,N′ - Bis(2,5 - di - tert - butylphenyl) - 3,4,9,10 - perylenedi- carboximide; BPPC). The mechanism of emission enhancement by doping of PBD into PAT has been discussed with different alkyl side-chain lengths. © 1997 John Wiley & Sons, Ltd.     

Blend of electroactive poly(3-dodecylthiophene) with comb-like alkylated polyacrylate

The conformational mode change of the stiff alkylated polymer, poly(3-dodecyl thiophene) (PDDT), with a flexible comb-like coil poly(octadecyl acrylate) (PODA), and the effect of intermolecular interaction between these two alkylated polymers with different chemical structure of the backbone were investigated using UV-Vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimeter (DSC), and wide-angle x-ray diffraction (WAXD). In addition to the characteristics of thermochromism, a homogeneous one phase was observed above 175°C when the PODA content was 10 wt % or less. Increased conductivity in the PDDT/PODA blend due to the highly conjugated π-system of PDDT backbone was observed in the presence of nonelectroactive PODA. A red-shift of absorption maximum of PDDT/PODA blend observed in solid state at room temperature. From the FTIR spectra, the gauche-trans conformational structure change of methylene units was investigated in two alkylated polymer blends. The increase of combined heat of fusion of the alkyl side chain melting of PDDT and the endothermic peak of PODA, as well as the interlayer d-spacing of PDDT main chain were also observed with the addition of PODA in blends. A more ordered conformational structure of rigid rod backbone of PDDT was induced due to the attractive intermolecular interaction which can cause cocrystallization between the alkylated side chains of two polymers. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 :1025–1041, 1997     

A study of the surface morphology of poly(p-phenylene terephthalamide) chars using scanning probe microscopy

The objective of this work was to investigate the changes in surface morphology associated with thermal degradation of poly(p-phenylene terephthalamide) (PPTA) into chars. To this end, PPTA samples decomposed at several temperatures up to 800 °C were studied on a local scale using atomic force microscopy (AFM) and scanning tunnelling microscopy (STM). Domains with a diameter of 40-50 nm started appearing among PPTA nanofibrils at about 500 °C. At this temperature and above, a film coating the fibre developed. This layer was much less rigid than PPTA, and remained deposited on the fibres, even at high temperatures. At 800 °C, the STM images showed a surface distribution typical of a carbonaceous material, isotropic although somewhat heterogeneous. When an intermediate isothermal step (500 °C, 200 min) was introduced along with heat treatment of PPTA under a constant rate, the material obtained at the end of this step was conductive enough to be studied by STM. Although the coating over the fibres also remained after the isothermal step, it was less homogeneous than in the absence of isothermal treatment. On further heating, the residue exhibited a surface morphology typical of a carbonaceous material, but much more homogeneous and isotropic than in the absence of the isothermal step.     

Swelling studies of crosslinked poly(p-phenylene terephthalamide) copolymers in sulfuric acid

In an attempt to improve the mechanical properties of extended chain polymers such as poly(p-phenylene terephthalamide) (PPTA), a crosslinkable terephthalic acid derivative (XTA) has been developed which can be incorporated into copolymers in various concentrations and activated after polymerization. The crosslinking of PPTA-co-XTA copolymer particles was investigated through a series of swelling experiments in concentrated H₂SO₄. The data show a systematic decrease in equilibrium swelling with increasing XTA content, indicating the XTA units are in fact acting as crosslink sites. Values for crosslink density were calculated from the Flory-Rehner theory of polymer swelling and compared with previous findings on crosslinked rigid polymer network systems. The effective number of crosslinks per XTA unit (efficiency) predicted by the Flory-Rehner theory increases and then decreases with % XTA. The decrease in crosslinking efficiency at high XTA concentrations is consistent with differential scanning calorimetry data which show the enthalpy of XTA reaction decreasing slightly with % XTA. The deviations at low % XTA may represent a failure of the Flory-Rehner theory to properly describe the rubbery elasticity of extended chain polymers. © 1994 John Wiley & Sons, Inc.