Fluorene oligomer with tetrathiafulvalenes as pendant groups: synthesis,electrochemical and spectroscopic properties

An oligomeric fluorene with pendant TTF units (OFT) was synthesized by the Yamamoto coupling reaction using Ni(COD)₂ as catalyst. The fluorescence spectra of fluorene-TTF (3a) and OFT displayed weak fluorescence intensity because of the photoinduced electron transfer (PET) interaction and energy transfer between the TTF and fluorene, while the fluorescence intensity would enhance significantly after chemical oxidation. The absorption spectra and cyclic voltammetry (CV) showed that an intramolecular interaction existed between the TTF and fluorene moieties in OFT, while in 3a such interaction could not be observed, due to the chain propagation of the fluorene backbone and an enhanced internal charge transfer interaction between the two electroactive moieties. Moreover, the conductivity showed that the doped OFT possessed a higher conductivity (1.4 × 10⁻³ S cm⁻¹) than the doped 3a (9.8 × 10⁻⁵ S cm⁻¹). These results demonstrated that OFT was a good candidate of fluorescence switches and conducting materials.     

Synthesis and photovoltaic properties of alternative copolymers of benzo[1,2-b:4,5-b′]dithiophene and thiophene

Two conjugated polymers containing benzodithiophene (BDT) unit and the unit of thiophene or thieno[3,2-b]thiophene, P(BDT-T) and P(BDT-TT), were synthesized by Pd-catalyzed Stille coupling method. The UV–Vis absorption, thermal, and electrochemical properties of the two polymers were characterized. Photovoltaic properties of the polymers were studied by using the polymers as donor and PC₇₀BM as acceptor with a weight ratio of polymer: PC₇₀BM of 1:1.5. The power conversion efficiencies of the PSC devices based on P(BDT-T) reached 2.05% with an open-circuit voltage of 0.75 V, a short-circuit current of 4.5 mA cm⁻², and a fill factor of 0.61, under the illumination of AM1.5, 100 mW cm⁻².     

Novel PEO-based solid composite polymer electrolytes with inorganic–organic hybrid polyphosphazene microspheres as fillers

Novel solid-state composite polymer electrolytes based on poly (ethylene oxide) (PEO) by using LiClO₄ as doping salts and inorganic–organic hybrid poly (cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS) microspheres as fillers were prepared. Electrochemical and thermal properties of PEO-based polymer electrolytes incorporated with PZS microspheres were studied. Differential scanning calorimetry (DSC) results showed there was a decrease in the glass transition temperature of the electrolytes and the crystallinity of the samples in the presence of the fillers. Maximum ionic conductivity values of 1.2 × 10⁻⁵ S cm⁻¹ at ambient temperature and 7.5 × 10⁻⁴ S cm⁻¹ at 80° were obtained and lithium ion transference number was 0.29. Compared with traditional ceramic fillers such as SiO₂, the addition of PZS microspheres increased the ionic conductivity of the electrolytes slightly and led to remarkable enhancement in the lithium ion transference number.     

Synthesis,characterization, and OFET characteristics of 3,4-diaryl substituted poly(thienylene vinylene) derivatives

Poly(thienylene vinylene) derivatives bearing aryl substituents at 3,4-positions have been synthesized in good yield by Stille-type polycondensation. Two types of aryl substituents, either a 4-octylphenyl or a 5-octyl-2-thienyl, were investigated in this study. The polymers were characterized by ¹H NMR, GPC, TGA, UV–vis absorption, and photoluminescence spectroscopy. The polymers (P1–P4) showed good to excellent solubility in common organic solvents, and UV–vis absorption spectra in solution exhibit maxima in the range of 511–595 nm. GPC analysis using PPP standards showed a number average molecular weight range of 6.59–8.98 × 10³ g mol⁻¹ for the various polymers. The field effect transistors based on these polymers were studied, and the results obtained are correlated to their molecular structure.     

Electrochemical investigation of Li–Al anodes in oligo(ethylene glycol) dimethyl ether/LiPF<Subscript>6</Subscript>

1 M LiPF₆ dissolved in oligo(ethylene glycol) dimethyl ether with a molecular weight 500 g mol⁻¹ was investigated as a new electrolyte (OEGDME500, 1 M LiPF₆) for metal deposition and battery applications. At 25 °C a conductivity of 0.48 × 10⁻³ S cm⁻¹ was obtained and at 85 °C, 3.78 × 10⁻³ S cm⁻¹. The apparent activation barrier for ionic transport was evaluated to be 30.7 kJ mol⁻¹. OEGDME500, 1 M LiPF₆ allows operating temperature above 100 °C with very attractive conductivity. The electrolyte shows excellent performance at negative and positive potentials. With this investigation, we report experimental results obtained with aluminum electrodes using this electrolyte. At low current densities lithium ion reduction and re-oxidation can be achieved on aluminum electrodes at potentials about 280 mV more positive than on lithium electrodes. In situ X-ray diffraction measurements collected during electrochemical lithium deposition on aluminum electrodes show that the shift to positive potentials is due to the negative Gibbs free energy change of the Li–Al alloy formation reaction.     

p-benzoquinone diimines and thiophene based alternating copolymers: organometallic catalyzed syntheses and elementary characterization

A series of alternating polymers, which were prepared by coupling of N, N’-dichloro-benzoquinonediimine (a) or 2, 5-dimethyl-N, N’-dichloro-benzoquinonediimine (b) with Grignard reagents of thiophene, were successfully prepared using Ni(II) complexes as catalyst with moderate yields (54–88%) and molecular weights (4.3–7.0 × 10³). The basic properties of the obtained copolymers were characterized by FT-IR, ¹H NMR, UV-vis absorption, cyclic voltammetry, thermal analysis and Gel permeation chromatography (GPC). The maximum UV–vis absorption of these polymers appears in the range of 410–430 nm and 437–494 nm in DMF and CF₃COOH, respectively. XRD patterns of these polymers suggest the low crystallinty. After doped by iodine, conductivity of obtained polymers was improved five-eight orders of magnitude relative to their corresponding neutral precursors (the conductivity of them was <10⁻¹³ S/cm). The electrochemical activity of iodine-doped polymers was greatly improved as compared to un-doped ones. The reduction of pristine benzoquinone polymers was also studied in order to tune their properties conveniently.     

Conductivity modification of proton conducting polymer gel electrolytes containing a weak acid (<Emphasis Type="Italic">ortho</Emphasis>-hydroxy benzoic acid) with the addition of PMMA and fumed silica

Polymer gel electrolytes synthesized by dispersing nano size fumed silica in polymer gel electrolytes containing polymethylmethacrylate (PMMA), ortho-hydroxy benzoic acid (o-OHBA) and dimethylacetamide (DMA) have been studied by complex impedance spectroscopy, viscosity and pH measurements. The addition of acid, polymer and fumed silica has been found to result in an increase in conductivity and viscosity of gel electrolytes and gels with conductivity higher than the corresponding liquid electrolytes have been obtained. Nano dispersed polymer gel electrolytes show conductivity 2.95 × 10⁻⁴ S cm⁻¹ and viscosity 1.74 × 10⁴ cP at 25 °C. Two maxima observed in the variation of conductivity of nano dispersed gels with fumed silica concentration have been assigned to the enhanced dissociation of weak acid and the formation of a high conducting interfacial region between fumed silica and gel electrolyte, respectively, which has also been supported by pH and viscosity studies. The small increase in conductivity of nano dispersed gels over the 20–100 °C temperature range and its constant value with time is suitable for devices.     

Ionic conductivity of swollen LDPE/poly(4-vinylpyridine) blend

Summary LDPE/P4VP films synthesized by in situ sorption and thermal polymerization of 4-vinylpyridine, (4VP), were used for conductivity investigations. The conductivities of swollen films varied from 7×10⁻⁶ to 1.21×10⁻³ S.cm⁻¹ at room temperature depending on P4VP mass increase in the host matrix. For the temperature range of 303–333K the conductivity varied from 7×10⁻⁶ to 2.66×10⁻³ S.cm⁻¹. A comparison between Arrhenius and VTF plots for conductivity measurements showed a best fit for temperature dependence according Arrhenius modified equation. The materials are stable for temperatures below 645 K. Received: 8 June 2001/ Revised version: 14 January 2002/ Accepted: 15 January 2002     

Preparation and electrochemical performance of gel polymer electrolytes with a novel star network

Well-defined star shaped polymers with α-Cyclodextrin (α-CD) core linking PMMA-block arms were synthesized by atom transfer radical polymerization (ATRP). Gel polymer electrolytes (GPEs) were prepared by encapsulating electrolyte solution of 1 mol L⁻¹ of LiClO₄/EC-PC (volume 1:1) into the obtained star shaped polymer host. The ionic conductivity of the GPEs and the cycling characteristics of LiCoO₂/GPEs/Graphite cell were studied by electrochemical impedance spectroscopy and charge-discharge testing, respectively. The results indicate that the GPEs have a high ionic conductivity up to 1.63 × 10⁻³ S cm⁻¹ at room temperature and exhibit a high electrochemical stability potential of 4.5 V (vs. Li/Li⁺). The discharge capacity of LiCoO₂/GPEs/Graphite cell is about 98% of its initial discharge capacity after 20 cycles at 0.1 C rate. Discharge capacity of the model cell with GPEs is stable with charge-discharge cycling.     

Nanocomposite hybrid membranes containing polyvinyl alcohol or poly(tetramethylene oxide) for fuel cell applications

New hybrid membranes containing polyvinyl alcohol (PVA) and poly(tetramethylene oxide) (PTMO) with heteropolyacid (HPA) as a hydrophilic inorganic modifier in an organic/inorganic matrix were developed for low-temperature proton exchange membrane fuel cells (PEMFCs). A maximum conductivity of 4.8 × 10⁻³ S cm⁻¹ was obtained at 80 °C and 75% RH for PVA/PWA/PTMO/H₃PO₄ (10/15/70/5 wt%), whereas the PVA/SiWA/MPTS/H₃PO₄ (50/10/10/30 wt%) membrane demonstrated a maximum conductivity of 8.5 × 10⁻³ S cm⁻¹ under identical conditions. These hybrid composite membranes were subsequently tested in a fuel cell. A maximum current density of 240 mA cm⁻² was produced at 70 °C for the PVA/PWA/PTMO/H₃PO₄ membrane, and the corresponding value for the PVA/SiWA/MPTS/H₃PO₄ membrane under identical conditions was 230 mA cm⁻². The small deviations in cell performance can be explained in terms of the variations in thickness of the membranes as well as differences in their conductivities. The fuel cell performances of these membranes decreased drastically when the temperature was increased to 100 °C.     

Synthesis and Electrical Properties of Three Novel Poly(Ferrocenyl-Schiff Bases) and Their Charge Transfer Complexes with Iodine

Three ferrocenyl-Schiff base monomers were synthesized by the condensation of ferrocenecarboxaldehyde and phenylenediamine under neutral conditions, and then used to produce copolymer materials with terephthaloyl chloride monomer by the Friedel–Crafts method. The model compound and copolymers of three novel poly(ferrocenyl-Schiff bases) and their charge transfer complexes with iodine were successful obtained and their structures were characterized by ¹H-NMR, infrared, and ultraviolet spectra. The effect of degree of iodine doping on their structures was studied. It appears that poly-p-bis(ferrocenyl-Schiff base) can be doped to a higher iodine level than the other two prepared materials. Electrical measurement results showed that the conductivity can be increased several orders of magnitude after doping with iodine. The maximum conductivity at room temperature is 3.17 × 10⁻⁴ S cm⁻¹ indicating that the conducting polymer has potential as a semiconductor material.     

Correlation of thermal properties and electrical conductivity of La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>Cu<Subscript>0.2</Subscript>Fe<Subscript>0.8</Subscript>O<Subscript>3−δ</Subscript> material for solid oxide fuel cells

A copper-doped ferrite with the chemical composition La_0.7Sr_0.3Cu_0.2Fe_0.8O_3−δ (LaSrCuFe) was prepared using the classical ceramics method starting from the oxides. The linear thermal expansion coefficient in air was measured in the temperature range between 550 and 1,250 K to be between 10 × 10⁻⁶ and 15 × 10⁻⁶ K⁻¹. The electrical conductivity in air was found to be higher than 100 S cm⁻¹ for temperatures lower than 1,100 K. A change of oxygen stoichiometry was found above 650 K in an atmosphere of 20 vol% oxygen with argon. This change can be correlated with the electrical conductivity.     

Polymer Electrolytes Based on Polymeric Ionic Liquid Poly(methyl 2-(3-vinylimidazolidin-1-yl)acetate bis(trifluoromethane sulfonyl)imide)

A new kind of ionic liquid monomer methyl 2-(3-vinylimidazolidin-1-yl)acetate bromide (MVIm-Br) and polymeric ionic liquid (PIL), poly(methyl 2-(3-vinylimidazolidin-1-yl)acetate bis(trifluoromethanesulfonyl)imide) (PMVIm-TFSI), were synthesized and characterized. Different compositions of polymer electrolytes were prepared by blending PMVIm-TFSI and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) with poly(methylmethacrylate-co-vinyl acetate) (P(MMA-VAc)). The thermal stability and ionic conductivity improved significantly when PMVIm-TFSI was added into P(MMA-VAc)/LiTFSI polymer. For the polymer electrolytes obtained, the highest ionic conductivity at 30 °C is 4.71 × 10⁻⁴ S cm⁻¹ and the corresponding decomposition temperature is ca. 308 °C. Moreover, P(MMA-VAc)/PMVIm-TFSI/LiTFSI electrolyte membrane (transmittance ≥90%) can be used as the ion-conductive layer material for electrochromic devices, which reveal excellent electrochromic performance.     

Polymeric ionic liquid membranes as electrolytes for lithium battery applications

A new kind of polymeric ionic liquid (PIL) membrane based on guanidinium ionic liquid (IL) with ester and alkyl groups was synthesized. On addition of guanidinium IL, lithium salt, and nano silica in the PIL, a gel PIL electrolyte was prepared. The chemical structure of the PIL and the properties of gel electrolytes were characterized. The ionic conductivity of the gel electrolyte was 5.07 × 10⁻⁶ and 1.92 × 10⁻⁴ S cm⁻¹ at 30 and 80 °C, respectively. The gel electrolyte had a low glass transition temperature (T _g ) under −60 °C and a high decomposition temperature of 310 °C. When the gel polymer electrolyte was used in the Li/LiFePO₄ cell, the cell delivered 142 mAh g⁻¹ after 40 cycles at the current rates of 0.1 C and 80 °C.     

Homogeneous electrocatalytic oxidation of <Emphasis Type="SmallCaps">d</Emphasis>-penicillamine with ferrocyanide at a carbon paste electrode: application to voltammetric determination

The electrooxidation of d-penicillamine (d-PA) was studied in the presence of ferrocyanide as a homogeneous mediator at the surface of a carbon paste electrode in aqueous media using cyclic voltammetry (CV) and chronoamperometry. Under optimum pH in CV the oxidation of d-PA occurs at a potential about 380 mV less positive than that in the absence of ferrocyanide. The catalytic oxidation peak current was dependent on the d-PA concentration and a linear calibration curve was obtained in the ranges 4.0 × 10⁻⁵–2.0 × 10⁻³ M and 8.0 × 10⁻⁶–1.8 × 10⁻⁴ M of d-PA with CV and differential pulse voltammetry (DPV) methods, respectively. The detection limits (3σ) were determined as 1.9 × 10⁻⁵ and 3.2 × 10⁻⁶ M by CV and DPV methods. This method was also used for the determination of d-PA in pharmaceutical preparations by the standard addition method.     

Ionic Transport Properties in Nanocrystalline Ce0.8A0.2O2-δ (with A = Eu,Gd, Dy,and Ho) Materials

The ionic transport properties of nanocrystalline 20 mol% Eu, Gd, Dy, and Ho doped cerias, with average grain size of around 14 nm were studied by correlating electrical, dielectric properties, and various dynamic parameters. Gd-doped nanocrystalline ceria shows higher value of conductivity (i.e., 1.8 × 10⁻⁴ S cm⁻¹ at 550°C) and a lower value of association energy of oxygen vacancies with trivalent dopants Gd³⁺ (i.e., 0.1 eV), compared to others. Mainly the lattice parameters and dielectric constants (ε_∞) are found to control the association energy of oxygen vacancies in these nanomaterials, which in turn resulted in the presence of grain and grain boundary conductivity in Gd- and Eu-doped cerias and only significant grain interior conductivity in Dy- and Ho-doped cerias.     

Synthesis and characterization of lithium holmium silicate solid electrolyte for high temperature lithium batteries

A new Li-ion conducting holmium based solid electrolyte by the sol–gel method was synthesized. The synthesis was carried out at low temperature compared to conventional methods by which lanthanoid silicates are synthesized. The formation temperature of the compound was found through differential thermal analysis and thermogravimetric analysis (DTA-TG). The sintered samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and ac impedance spectroscopy. The temperature dependence of conductivity was analysed. The experimental results show that the formation temperature of the lithium holmium silicate was found to be above 500 °C. Highest conductivity obtained was in the order of 10⁻⁴ S cm⁻¹ at 750 °C.     

Influence of nanoscale NiO on magnetic and electrochemical behavior of PVDF-based polymer nanocomposites

New poly(vinylidene fluoride) (PVDF)/NiO-based polymer nanocomposites were prepared by phase inversion method, using dimethyl formamide as solvent and deionized water as non-solvent. The structure and porous morphology of the membranes were studied by field emission scanning electron microscopy. The presence of NiO resulted in overall decrease in porosity and crystallinity of the nanocomposite membranes. Using electrochemical impedance spectroscopy, a maximum ionic conductivity of 1.08 × 10⁻³ S cm⁻¹ was obtained for PVDF membrane with 1 wt% content of NiO. The good efficiency of conductivity observed in the membrane was explained on the basis of decrease in crystallinity and movement of charge carriers in NiO structure. The magnetization of nanocomposite membranes gradually increased with increase in NiO content.     

Synthesis of functionalized copolymer electrolytes based on polysiloxane and analysis of their conductivity

Functionalized siloxane-based solid polymer electrolytes were synthesized using a platinum-catalyzed silylation reaction. The ionic conductivities of these solid polymer electrolytes were measured as a function of the concentration of lithium bis(trifluoromethylsulfonyl)imide (LiTFSi) salt. The highest ionic conductivity and lowest activation energy of solid polymer electrolytes were observed to be 1.15 × 10⁻⁴ S cm⁻¹ (25 °C) and 3.85 kJ mol⁻¹, respectively. The interface property between electrolyte and electrode and thermal stability of the polymer electrolytes were found to enhance after they were functionalized with acrylate, and the functionalized electrolytes were observed to maintain a glass transition temperature as low as that of other siloxane compounds. Thus, modifications involving acrylate with ethylene oxide group substitution provide a route for carrier ions and enhance both the ionic conductivity and mechanical properties of the siloxane structure.     

Synthesis and characterization of the novel inimer-containing fluorene units and preparation of blue light-emitting polymers

The novel inimer-containing fluorene units was successfully synthesized and characterized. Hyperbranched homopolymer and copolymers with methyl methacrylate (MMA) were prepared by the novel inimer via atom transfer radical polymerization where CuBr/1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA) were used as catalyst. The copolymerization of inimer and MMA was performed under different ratio of the initial inimer/MMA and the inimer acted as not only the branched point (BP) but also the functional groups which emit blue light. The number-average molecular weight (M _n) and polydispersity index (PDI) of polymers are in the ranges (3.6–18.4) × 10³ and (1.3–2.8), respectively. Thermal gravimetric analysis (TGA) results showed all polymers had good thermal stabilities. The number of the inimers acted as branched point in the copolymer backbone is estimated by ¹H NMR spectra and UV–Vis absorption spectra.