Polypyrrole-palladium systems prepared in PdCl2 aqueous solutions

In the work, reactions of a partially deprotonated polypyrrole doped with hydroxide ions (PPyOH) in various PdCl₂ aqueous solutions which differed in acidity were studied. Using X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy it was established that in the PdCl₂ solutions of lower acidity PPyOH was oxidatively doped and Pd⁰ and Pd²⁺ were incorporated into the polymer matrix. Pd²⁺ formed palladium(II) hydroxy-and/or aquochlorocomplex dopant anions and/or was coordinated by nitrogen atoms of the polymer (Pd-N bond). Additionally, deprotonation of PPyOH occurred in the PdCl₂ solutions of lower acidity. It was proposed that deprotonation of PPyOH was caused by nucleophilic attack of [PdCl₃(H₂O)]⁻ on the positively charged, doped polymer chain. By comparison of the PPyOH and chloride-doped polypyrrole (PPyCl)-palladium systems prepared in similar PdCl₂ solutions of lower acidity it was shown that the type of the counterion in the starting polymer has a decisive effect on the deprotonation process.PPyOH was less reactive towards palladium species in the PdCl₂ solutions of higher acidity where [PdCl₄]²⁻ was the dominant complex. PPy-palladium systems containing exclusively Pd²⁺ were obtained in this case. It was proposed that incorporation of palladium species in these conditions proceeded via an acid-base reaction or coordination of palladium ions by the polymer chain (Pd-N bond formation).Results of the studies may serve as the basis for the preparation of a variety of polypyrrole-supported palladium catalysts.     

Conductivity and thermal behavior of proton conducting polymer electrolyte based on poly (N-vinyl pyrrolidone)

The polymer electrolytes based on poly N-vinyl pyrrolidone (PVP) and ammonium thiocyanate (NH₄SCN) with different compositions have been prepared by solution casting technique. The amorphous nature of the polymer electrolytes has been confirmed by XRD analysis. The shift in T_g values and the melting temperatures of the PVP-NH₄SCN electrolytes shown by DSC thermo-grams indicate an interaction between the polymer and the salt. The dependence of T_g and conductivity upon salt concentration have been discussed. The conductivity analysis shows that the 20 mol% ammonium thiocyanate doped polymer electrolyte exhibit high ionic conductivity and it has been found to be 1.7 × 10⁻⁴ S cm⁻¹, at room temperature. The conductivity values follow the Arrhenius equation and the activation energy for 20 mol% ammonium thiocyanate doped polymer electrolyte has been found to be 0.52 eV.     

The electrical conductivity of doped oligo[aromatic diimidoselenide]

DC electrical conductivity of oligo[aromatic diimidoselenide] is studied in the temperature range 300-500 K after doping. The dopants used are I₂, FeCl₃, ZnCl₂, NaClO₄ and CuSO₄. Doping is done by mixing with 10% of the dopant, and by chemical doping. The DC electrical conductivity of the two types of doped materials is measured, compared and results interpreted. A trend of high DC electrical conductivity in the case of chemical doping especially with I₂ has been noticed. A conduction of 10⁻⁷ S cm⁻¹ is obtained at ambient or higher temperatures. This is related to a charge transfer complex formation between the oligomers and I₂. The complexation is confirmed from the electronic spectra of the chemically doped materials which showed a decrease in the π-π^* energy absorption bands and an increase in the n-π^* energy absorption bands.     

Crystal Structures, and Electrical Conducting and Magnetic Properties in the Plate Crystals of (Ethylenedithiotetrathiafulvalenoquinone-1,3-dithiolemethide)2·MX4 (M=Fe, Ga, X=Br; M=Fe, X=C1) Salts

By the reaction of a new donor molecule, ethylenedithiotetrathiafulvalenoquinone-1,3-dithiolemethide (1) with FeBr₃, GaBr₃ or FeCl₃ in CH₃CN/CS₂ charge transfer (CT) salts of 1 with counteranions of FeBr₄⁻, GaBr₄⁻ or FeCl₄⁻ (1₂·FeBr₄, 1₂·GaBr₄ and 1₂·FeCl₄) as plate crystals were obtained. Their crystal structures are apparently similar to each other, in which 1 molecules are dimerized in the parallel direction of their molecular long axes, and the dimers are stacked with changing the direction of the molecular long axes alternately to form a one- dimensional column. The counteranions intervene between the 1-stacked columns and are aligned in a zigzag manner. The room-temperature electrical conductivities of 1₂·FeBr₄ and 1₂·GaBr₄ are fairly high (10-15 S cm⁻¹), but a small value (0.8 S cm⁻¹) is obtained for 1₂·FeCl₄. For all CT salts, temperature dependences of electrical conductivity are semiconducting in spite of very small activation energies (30-90 meV). Based on the comparison between their electrical conducting and magnetic properties, it is suggested that the d spins of FeBr₄⁻ or FeCl₄⁻ ions exert almost no influence on the π conducting electrons in the 1-stacked column.     

Quantitative determination of site occupancy of multi-rare-earth elements doped into Ca2SnO4 phosphor by electron channeling microanalysis

X-ray fluorescence analysis based on electron channeling effects in transmission electron microscopy (TEM) was performed on Ca₂SnO₄ phosphor materials doped with Eu³⁺/Y³⁺ at various concentrations, which showed red photoluminescence associated with the ⁵D₀-⁷F₂ electric dipole transition of Eu³⁺ ions. The method provided direct information on which host element site dopant elements occupy, the results of which were compared with those of X-ray diffraction (XRD)-Rietveld analysis. The obtained results indicated that while it is not favorable for a part of Eu³⁺ to occupy the smaller Sn⁴⁺ site, this is still energetically better than creating Ca vacancies or any other of the possible charge balance mechanisms. The local lattice distortions associated with dopant impurities with different ionic radii were also examined by TEM-electron energy-loss spectroscopy (TEM-EELS). The change in PL intensity as a function of dopant concentration is discussed based on the experimental results, although the general concept of concentration quenching applies.     

Competition between dopants on redox reaction of polypyrrole

The surface of PPy prepared in a multiple electrolyte solution such as NaDS-NaClO₄ in H₂O shows a coarser structure than that of the polymer prepared in a single electrolyte system. DS⁻ with a large aliphatic chain is used as a dopant in preparation of PPy. The dopant is trapped in PPy when the polymer is reduced in an aqueous system. A cation Na⁺ or K⁺ is inserted into the polymer to balance the free DS⁻ liberated form and remained in it on reduction. PPy doped with DS⁻ shows a high degree of redox reactivity in the system of TBADS-AN but a poor stability in repeated redox process. The degree and rate of redox reactivity enhance when an aqueous solution of NaClO₄ is used as an electrolyte system. Both Na⁺ and ClO₄⁻take part in the redox reaction and the reduction process is intense at only one current potential.     

Chiral polymer hosts for circularly polarized electroluminescence devices

Polymer electroluminescence devices producing circularly polarized luminescence (CP PLEDs) have valuable photonic applications. The fabrication of a CP PLED requires a polymer host that provides the appropriate chiral environment around the emitting dopant. However, chemical strategies for the design of chiral polymer hosts remain underdeveloped. We have developed new polymer hosts for CP PLED applications. These polymers were prepared through a free-radical polymerization of 3-vinylcarbazole with a chiral N-alkyl unit. This chiral unit forces the carbazole repeat units to form mutually helical half-sandwich conformers with preferred (P)-helical sense along the polymer main chain. Electronic circular dichroism measurements demonstrate the occurrence of chirality transfer from chiral monomers to achiral monomers during chain growth. The (P)-helical-sense-enriched polymer interacts diastereoselectively with an enantiomeric pair of new phosphorescent (R)- and (S)-dopants. The magnitude of the Kuhn dissymmetry factor (g_abs) for the (P)-helically-enriched polymer film doped with the (R)-dopant was found to be one order of magnitude higher than that of the film doped with the (S)-dopant. Photoluminescence dissymmetry factors (g_PL) of the order of 10⁻³ were recorded for the doped films, but the magnitude of diastereomeric enhancement decreased to that of g_abs. The chiral polymer host permits faster energy transfer to the phosphorescent dopants than the achiral polymer host. Our photophysical and morphological investigations indicate that the acceleration in the chiral polymer host is due to its longer Förster radius and improved compatibility with the dopants. Finally, multilayer CP PLEDs were fabricated and evaluated. Devices based on the chiral polymer host with the (R)- and (S)-dopants exhibit electroluminescence dissymmetry factors (g_EL) of 1.09 × 10⁻⁴ and −1.02 × 10⁻⁴ at a wavelength of 540 nm, respectively. Although challenges remain in the development of polymer hosts for CP PLEDs, our research demonstrates that chiroptical performances can be amplified by using chiral polymer hosts.

Polymer electroluminescence devices producing circularly polarized luminescence (CP PLEDs) have valuable photonic applications.     

Degradation of polychloroprene/natural rubber (PCP/NR) blends by photo-Fenton process

The effect of light and FeCl₃·6H₂O on polychloroprene (PCP)/natural rubber (NR) blends in toluene solution were investigated to demonstrate the influence of each polymer on the degradation process. The contributions of total polymer concentration (C_p), temperature (T) and polychromatic light exposure (L) on the degradation process were investigated through a 2³ factorial design approach. Degradation kinetics was examined by solution viscosity time data. FTIR spectroscopy and TGA were used to characterize the degradation. The exposure of the PCP/NR blend solution containing FeCl₃·6H₂O to light induces degradation in the polymers. A decrease of up to 70% in solution efflux time at constant temperature and without aggregation or phase separation was observed. PCP degradation by-products amplify the degradation of NR, as evidenced by the decrease in the PCP/NR 1:99 (w/w) solution efflux time, which was larger than that of the pure NR solution. The film cast from the solution exposed to light was thermally less stable than the one which was cast without FeCl₃·6H₂O.     

Experimental studies on the ring opening polymerization of p-dioxanone using an Al(OPr)3-monosaccharide initiator system

The ring opening polymerization (ROP) of p-dioxanone using a protected monosaccharide (1,2;3,4-di-O-isopropylidene-α-d-galactopyranose)/Al(OⁱPr)₃ initiator system to yield polydioxanone with a protected monosaccharide end-group is described. The products were synthesized at 60-100 °C and characterized by ¹H and ¹³C NMR, and MALDI-TOF mass spectrometry. Besides the desired polydioxanone functionalised with a monosaccharide end-group, also polydioxanone with an OⁱPr end-group was formed (20-30%). Systematic studies showed that the polymer yield is a function of the reaction temperature and the reaction time, with higher temperatures (100 °C) leading to lower yields. The average chain length of the polymers is between 7 and 58 repeating units and may be tuned by the monomer to monosaccharide ratio (at constant Al(OⁱPr)₃ intake). A statistical model has been developed that successfully describes the experimentally observed relation between the average chain length of the functionalized polymer and reaction parameters.     

Effects of glass-transition temperature on properties of photorefractive polymer composite

In this study, photorefractive polymer composites were developed in which polycarbonate was doped with a dual-function dopant and a photocharge generation sensitizer. The dual-function dopant has the function of providing both charge transport and optical nonlinearity. The composites' photoconductivity and electrooptic coefficient were investigated experimentally. The effects of the glass-transition temperature (T_g), dual-function dopant content, and electric field on the composites' photorefractive properties were studied as well. The results show that the composites' photorefractive properties are enhanced with decreasing T_g, increasing dual-function dopant content, and increasing electric field. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3302–3306, 1999     

Synthesis of a new donor, BEDT-HBDST and crystal structures, electrical and magnetic properties of (BEDT-HBDST)2MX4 (M=Fe, Ga, X=Cl, Br), where BEDT-HBDST=2,5-bis(4,5-ethylenedithio-1,3-diselenol-2-ylidene)-2,3,4,5-tetrahydrothiophene

A novel conjugation-elongated bis(ethylenedithio)tetraselenafulvalene (BETS) type donor, 2,5-bis(4,5-ethylenedithio-1,3-diselenol-2-ylidene)-2,3,4,5-tetrahydrothiophene (BEDT-HBDST) and its magnetic and non-magnetic anion salts, (BEDT-HBDST)₂MX₄ (MX₄⁻=FeCl₄⁻, GaCl₄⁻, FeBr₄⁻ and GaBr₄⁻), were prepared. These four salts are isostructural and belong to the space group of P2/c. They showed semiconducting behavior with small activation energies (59-64 meV). The band structures of these salts are quasi one-dimensional and there is a midgap between the upper band and the lower band, since the degree of dimerization is significant in the stacking direction. The MX₄⁻ ions are located between the donor columns and near to the ethylenedithio moieties of the donor molecules. The magnetic susceptibilities of the FeCl₄⁻ and FeBr₄⁻ salts follow the Curie-Weiss law with Curie constants of 4.6 and 4.8 emu K mol⁻¹ (sum of the spins of S=5/2 and S=1/2) and negative Weiss temperatures of θ=−1.2 and −4.9 K, respectively, revealing a weak antiferromagnetic interaction of 3d spins of the FeCl₄⁻ and FeBr₄⁻ anions. The Fe?Fe (6.66-7.60 Å), Cl?Cl (4.81-4.82 Å) and Br?Br (4.74-4.77 Å) distances in the crystal structures of these salts are significantly long. Therefore, the direct magnetic interaction between the 3d spins of the nearest neighboring Fe³⁺ ions appears to be not readily accessible.     

XPS Studies of PtCl4 and H2PtCl6·6H20 doped polyacetylene

The PtCl₄ and H₂PtCl₆-6H₂O doped polyacetylene were studied by X-ray photoelection spectroscopy and transmission electron microscopy. We found that both Pt 4f and Cl 2p peaks could be resolved into two components both with a splitting of ca. 1.5 eV. The higher binding energy components of Pt 4f peak is attributed to Pt⁴⁺ and the lower binding energy one to Pt²⁺ species. From quantitative analysis of the results of decomposition of both Pt 4f and Cl 2p peaks it was found that an atomic ratio of chlorine to platinum for Pt²⁺ species is (Cl) / (Pt) = 2 and that for Pt⁴⁺ species is (Cl) / (Pt) = 6 for both PtCl₄ and H₂PtCl₆·6H₂O doped polyacetylene. The C 1s peaks could be decomposed into two components separated by ca. 1 eV. The intensity of the higher binding energy component increased with increasing dopant concentration. These indicate that the platinum salt doping proceeds through charge transfer from polyacetylene chain to platinum atom resulting in a partial reduction from Pt⁴⁺ to Pt²⁺ state. The existence of PtCl₂ cluster on the surface of the doped polyacetylene film was supported by transmission electron microscopy and electron diffraction observations. These results indicate that a random distribution of the dopant along the macromolecular chain, and the charge per carbon atom in the metallic region of doped polyacetylene has been estimated to be 0.2 |e|. From these results the mechanism of the PtCl₃ and H₂PtCl₆·6H₂O doping process in polyacetylene is clarified as follows: Thus the dopant anion in polyacetylene is PtCl,^2? for both PtCl₄ and H₂PtCl₆·6H₂O doping.     

Synthesis and characterization of a new network polymer electrolyte containing polyether in the main chains and side chains

A new network polymer electrolyte matrix with polyether in the side chains and main chains was synthesized by the azo-macroinitiator method and urethane reaction. The macroinitiator, polymer and network polymer were confirmed by Fourier-transform infrared (FT-IR) spectroscopy and ¹H NMR. FT-IR was also used to study the environment of lithium ions doped in these network polymer electrolytes. Three important groups are considered: N-H, carbonyl, and ether groups. The thermal properties of the polymer electrolytes were measured by differential scanning calorimetry and thermogravimetric analysis. The T_g value of this polymer is less than that of a general comb-like polymer. Added lithium ions interact with the oxygen atoms on ether groups, causing the T_g of the polymer electrolyte to increase. Moreover, the interaction between lithium ions and ether groups decreases the decomposition temperature of the polymer. The conductivity measured by AC impedance reached a maximum of 10⁻⁴ S cm⁻¹. A plot of conductivity vs. temperature fit the Vogel-Tamman-Fulcher equation, indicating that ionic mobility in this network polymer electrolyte is coupled to segmental chain movements.     

Polybithiophene Heterogeneity: A Differential Cyclic Voltabsorptometry Study

The redox behavior of polybithiophene in 0.1 M Bu₄NBF₄ solutions in acetonitrile is studied using cyclic voltammetry, potentiostatic spectroelectrochemical measurements, and differential cyclic voltabsorptometry. Comparing differential cyclic voltabsorptograms, obtained at wavelengths of 420, 475, and 520 nm for the undoped state and 720, 850, and 1050 nm for the doped state, with the cyclic voltammetry data reveals the polymer heterogeneity. The heterogeneity of the undoped polymer is ascribed to the formation of polymer chains of different lengths during the polybithiophene synthesis. The heterogeneity of the doped polymer is attributed to the existence of two types of an oxidized state. Both states presumably form as the result of the occurrence of two parallel processes. The first oxidized state is probably connected with the formation of a strong complex (associate) of positively charged fragments of a polymer chain with the dopant anion, while the second oxidized state is caused by a weak interaction between the dopant and the doped polymer.     

Ellipsometric investigations of Fe3+-doped polyvinyl alcohol films

In this work, we study the inclusion mechanism of Fe³⁺ ions in a polyvinyl alcohol (PVA) matrix. Thin films of pure and FeCl₃-doped PVA on silicon substrates, prepared by the spin-coating method, are investigated using spectroscopic ellipsometry (SE) and Fourier transform infrared (FT-IR) spectroscopy. SE measurements of PVA and Fe³⁺-doped thin films are carried out at an incidence angle of 75° over the wavelength range of 0.24–1.1 μm. An optical model is used to obtain the refractive index (n) and the extinction coefficient (k). The gap energy E _g is afterwards evaluated. The Fe³⁺ doping is found to affect strongly the optical parameters of the polymer films. In fact, an increase in the refractive index with doping is observed, resulting from the intermolecular hydrogen bonding between Fe³⁺ ions with the adjacent OH group of PVA. The increase of the thin films' absorption with doping is estimated by the k spectral profile analysis. The gap energy is then calculated and shows an important decrease with the Fe³⁺ filling, more pronounced for low doped samples. Such a behavior is confirmed by FT-IR analysis.     

MÖSsbauer Spectroscopic Study of Fecl3 Complexes of Poly(N-Methyl-2,5-Pyrrolylene), Poly(2,5-Thienylene), and Poly(3-Methyl-2,5-Thienylene) Prepared by Ni-Catalyzed Polycondensation

Reaction of FeCl₃ with poly(N-methyl-2,5-pyrrolylene) (PNMPy), poly(2,5-thienylene) (PTh), and poly(3-methyl-2,5-thienylene) (P3MeTh) caused reduction of FeCl₃ to afford Fe²⁺ species. Variable temperature Mössbauer spectra of the reaction systems indicated formation of FeCl₂ and FeCl^? ₄. The latter is regarded as a counter-anion for the cation delocalized along the π-conjugated polymer chain.     

The effect of Ce3+ cations on polyaniline morphology and electric properties

Polyaniline (PANI) is synthesized in the potentiostatic pulse mode from an electrolyte containing Ce₂(SO₄)₃. Cations Ce³⁺ are incorporated into the polymer composition during PANI redox transformations. It is shown that PANI in its conducting and dielectric forms contains different amounts of Ce³⁺ cations. Starting with the beginning of polymerization, the Ce³⁺ cations actively form the special polymer morphology as demonstrated by SEM images. The chief consequence of the formation of so well-developed uniform nanostructure is that the latter allows the dopant anions, cations, and protons to easily enter and leave it. This, in turn, results in the high electrochemical activity of this polymer and enhances the conductivity of PANI samples doped with Ce³⁺ cations as compared with those doped with only protons.     

Synthesis of polypyrrole micro/nanofibers via a self-assembly process

Novel polypyrrole (PPy) micro/nanofibers were synthesized via a self-assembly process by using 4-hydroxy-3-[(4-sulfo-1-naphthalenyl) azo]-1-naphthalenesulfonic acid (Acid Red B) as dopant and ferric chloride (FeCl₃) as oxidant. Experimental conditions, including the concentration of the dopant, reaction temperature and stirring state have been investigated for their influences on the morphology of the synthesized PPy micro/nanofibers. The products were characterized by scanning electron microscopy, transmission electron microscopy and Fourier-transform infrared spectroscopy. The formation mechanism of micro/nanofibers was studied. It is believed that the micelles formed by the dopant and pyrrole monomer act as templates during the synthesis process. Two functions of aggregation and synthesis are proposed in the reaction system simultaneously, and the morphologies of micro/nanofibers are the co-operations of these two functions. The maximum conductivity value of the PPy micro/nanofibers was 8.56 S cm^?1     

金属氧化物掺杂改善LiFePO4电化学性能

采用氧化物前驱体对磷酸铁锂(LiFePO₄)进行少量金属离子掺杂，并用XRD，SEM和恒电流充放电对掺杂的LiFePO₄进行了研究。结果表明，少量的掺杂离子在很大程度上提高了LiFePO₄的电化学性能，特别是大电流放电性能。1.0 mol%的Nb⁵⁺掺杂LiFePO₄的0.1 C放电容量约150 mAh·g^-1；即使在3 C倍率下放电，也有117 mAh·g^-1的容量。掺杂的效果与掺杂离子的半径、价态密切相关，半径小、价态高的离子对提高LiFePO₄的电化学性能有利。在掺杂量较小时(<2.0 mol%)，掺杂效果与掺杂离子的浓度关系不大。