Phenylene vinylene-based electroluminescent polymers with electron transport block in the main chain

We report a new route for the design of soluble phenylene vinylene (PV) based electroluminescent polymers bearing electron-deficient oxadizole (OXD) and triazole (TZ) moieties in the main chains with the aryloxy linkage. Both series of the PV-based polymers were prepared by Wittig reaction. By properly adjusting the OXD and/or TZ content through copolymerization, we can achieve an enhanced balance of hole- and electron injections, such that the device efficiency is significantly improved. Light-emitting diodes fabricated from P1, P2, P3, P4, P5, P6, and P7 with the configuration of Indium-Tin Oxide (ITO)/Poly (styrene sulfonic acid) doped poly (ethylenedioxythiophene) (PEDOT)/polymer/Ca/Al, emit bright green light with the maximum peak around 500 nm. For the device using the optimal polymer (P4) as emitting layer, a maximum brightness of 1300 cd/m(2) at 20 V and a maximum luminance efficiency of 0.325 cd/A can be obtained.

Syntheses, structure and ethylene polymerization behavior of beta-diiminato titanium complexes

A series of new titanium complexes bearing beta-diiminato ligands [(Ph)NC(R-1)CHC(R-2)N(Ph)](2)TiCl2 (4a: R-1 = R-2 = CH3; 4b: R-1 = R-2 = CF3; 4c: R-1 = Ph, R-2 = CH3; 4d: R-1 = Ph, R-2 = CF3) has been synthesized and characterized. X-ray crystal structures reveal that complexes 4a and 4c adopt distorted octahedral geometry around the titanium center. With modified methylaluminoxane (MMAO) as a cocatalyst, complexes 4a-d are active catalysts for ethylene polymerization, and produce high molecular weight polyethylenes. Catalyst activities and the molecular weights of polymers are considerably influenced by the steric and electronic effects of substituents on the catalyst backbone under the same polymerization condition. With the strong electron-withdrawing groups (CF3) at R-1 or/and R-2 position, complexes 4b and 4d show higher activities than complexes 4a and 4c, respectively.

A Monte Carlo simulation for the micellization of ABC 3-miktoarm star terpolymers in a selective solvent

We have used Monte Carlo simulation to study the micellization of ABC 3-miktoarm star terpolymers in a selective solvent (good to A segment, bad to B and C segments). The simulation results reveal that the self-assembled morphology is determined by the block length, molecular architecture, terpolymer concentration and insolubility of insoluble block in the solvent. In dilute solution, symmetric terpolymers (N-B = N-C = 30) tend to aggregate into a novel wormlike pearl-necklace structure linked by an alternating arrangement of B and C spheres, whereas the asymmetric terpolymers (NB = 10, NC = 50) are likely to aggregate into spherical or cylindrical micelles (formed by C blocks) connected with some small B spheres, when the concentration of terpolymer is relatively low (chain number is 100). However, when the concentration of terpolymer is relatively high (chain number is 250), the symmetric terpolymers tend to aggregate into a netlike structure linked by an alternation of B and C spheres, whereas the asymmetric terpolymers are likely to aggregate into wormlike micelles (formed by C blocks) connected with some of small spheres (formed by B blocks). Moreover, when the insolubility of insoluble block in the solvent is weak, the insoluble blocks aggregate into some incompact micelles.

Titanium and zirconium complexes with aminoiminophosphorane ligands

A series of titanium and zirconium complexes based on aminoiminophosphorane ligands [Ph2P(Nt-Bu)(NR)](2)MCl2 (4, M = Ti, R = Ph; 5, M = Zr, R = Ph; 6, M = Ti, R = SiMe3; 7, M = Zr, R = SiMe3) have been synthesized by the reaction of the ligands with TiCl4 and ZrCl4. The structure of complex 4 has been determined by X-ray crystallography. The observed very weak interaction between Ti and P suggests partial pi-electron delocalization through both Ti and P. The complexes 4-7 are inactive for ethylene polymerization in the presence of modified methylaluminoxane (MMAO) or i-Bu3Al-Ph3CB(C6F5)(4) under atmospheric pressure, and is probably the result of low monomer ethylene concentration and steric congestion around the central metal.

Thermotropic liquid crystallinity, thermal decomposition behavior, and aggregated structure of poly(propylene carbonate)/ethyl cellulose blends

Maleic anhydride end capped poly(propylene carbonate) (PPC-MA) was blended with ethyl cellulose (EC) by casting from dichloromethane solutions. The thermotropic liquid crystallinity, thermal decomposition behavior, and aggregated structure were investigated by differential scanning calorimetry (DSC), thermogravimetry (TGA), and wide angle X-ray diffraction (WAXD). DSC exhibits thermotropic liquid crystallinity in the rich EC composition range. TGA shows that thermal decomposition temperatures were elevated upon interfusing EC into PPC-MA. WAXD corroborates that EC and PPC-MA/EC blend films cast from dilute dichloromethane solution possessed cholesteric liquid crystalline structure in the rich EC composition range, and that dilution of PPC-MA with EC increased the dimension of noncrystalline region, leading to a more ordered packed structure.

Electron effect of p-substituent on iron(II) and cobalt(II) pyridinebisimine catalyst for ethylene polymerization

A series of 2,6-bis(imino)pyridyl iron and cobalt complexes bearing p-substituent [2,6-(ArN=CMe)(2)C5H3N]-MCl2 (Ar=2,6-Me2C6H3, 2,4,6-Me3C6H2, 2,6-Me-2-4-BrC6H2, 2,6-Me-2-4-ClC6H2, 2,4-Me-2-6-BrC6H2, 2,4-Me-(2)-6-ClC6H2, while M=Fe, Co) have been synthesized and investigated as catalysts for ethylene polymerization in the presence of modified methylaluminoxane as a cocatalyst. The electron effect and positions of the substitueni of pyridinebisimine ligands were observed to affect considerably catalyst activity and polymer property.

A rapid solid-phase synthesis to soluble oligothiophene molecular wires

A novel method for the preparation of oligothiophene molecular wires is described via a bi-directional solid-phase synthesis. Using an alternating sequence of bromination and Stille coupling reactions, oligomers were obtained up to the heptamer in excellent yield and purity.

New neutral nickel(II) complexes bearing pyrrole-imine chelate ligands: synthesis, structure and norbornene polymerization behavior

New neutral nickel(II) complexes bearing nonsymmetric bidentate pyrrole-imine chelate ligands (4a-d), [2-(ArNCH)C4H3N]Ni(PPh3)Ph [Ar=2,6-diisopropylphenyl (a), 2-methyl-6-isopropylphenyl (b), 2,6-diethylphenyl (c), 2-tert-butylphenyl (d)], have been prepared in good yields from the sodium salts of the corresponding ligands and trans-Ni(PPh3)(2)(Ph)Cl, and the structure of complex 4a has been confirmed by X-ray crystallographic analysis. These neutral Ni(II) complexes were investigated as catalysts for the vinylic polymerization of norbornene. Using modified methylaluminoxane (MMAO) as a cocatalyst, these complexes display very high activities and produce great mass polymers. Catalyst activity of up to 4.2 x 10(7) g (mol Ni h)(-1) and the viscosity-average molecular weight of polymer of up to 9.2 x 10(5) g mol(-1) were observed. Catalyst activity, polymer yield, and polymer molecular weight can be controlled over a wide range by the variation of reaction parameters such as Al-Ni ratio, norbornene-catalyst ratio, monomer concentration, polymerization reaction temperature and time.

Crystallization and melting behaviors of PPC-BS/PVA blends

The isothermal crystallization and melting behaviors of poly(propylene carbonate) end-capped with benzenesulfonyl/poly (vinyl alcohol) (PPC-BS/PVA) blends over rich PVA composition range were first investigated by differential scanning calorimetry (DSC). PPS-BS/PVA interaction parameter, chi(12), calculated from equilibrium melting temperature depression was -0.44, revealing miscibility of PPC-BS with PVA in the melt and favorable interactions. The temperature dependence of crystallization rate constant at initial crystallization stage was analyzed using the modified Lauritzen-Hoffman expression. The chain width, a(0), the thickness of a monomolecular layer, b(0), the fold and lateral surface-free energies, sigma(e) and sigma, and the work of chain folding, q, for neat PVA were first reckoned to be 4.50 Angstrom, 4.78 Angstrom, 76.0 erg.cm(-2), and 4.70 kcal.mol(-1), respectively. The values of sigma(e) and q for PVA in PPC-BS/PVA blends exhibited a maximum in the neighborhood of 10/90 PPC-BS/PV, respectively.

Synthesis and characterization of maleated poly(3-hydroxybutyrate)

Graft copolymerization of maleic anhydride (MA) onto poly(3-hydroxybutyrate) (PHB) was carried out by use of benzoyl peroxide as initiator. The effects of various polymerization conditions on graft degree were investigated, including solvents, monomer and initiator concentrations, reaction temperature, and time. The monomer and initiator concentrations played an important role in graft copolymerization, and graft degree could be controlled in the range from 0.2 to 0.85% by changing the reaction conditions. The crystallization behavior and the thermal stability of PHB and maleated PHB were studied by DSC, WAXD, optical microscopy, and TGA. The results showed that, after grafting MA, the crystallization behavior of PHB was obviously changed. The cold crystallization temperature from the glass state increased, the crystallization temperature from the melted state decreased, and the growth rate of spherulite decreased. With the increase in graft degree, the banding texture of spherulites became more distinct and orderly. Moreover, the thermal stability of maleated PHB was obviously improved, compared with that of pure PHB.

Thermal degradation kinetics of uncapped and end-capped poly(propylene carbonate)

In order to improve its thermal stability, poly(propylene carbonate)(PPC) was end-capped by different active agents. Thermogravimetric data show that the degradation temperature of uncapped PPC was lower than that of end-capped PPC. The kinetic parameters of thermal degradation of uncapped and end-capped PPC were calculated according to Chang's method. The results show that different mechanisms operate during the whole degradation temperature range for uncapped PPC. In the first stage, chain unzipping dominates the degradation. With increasing temperature, competing multi-step reactions occur. In the last stage, random chain scission plays an important role in degradation. For end-capped PPC, random chain scission dominates the whole degradation process.

A wide-bandgap semiconducting polymer for ultraviolet and blue light emitting diodes

A novel wide-bandgap conjugated polymer (PDHFSCHD) consisting of alternating dihexylfluorene and rigidly twisted biphenyl units has been synthesized. The new fluorene-based copolymer composed of rigid twisting segments in the main-chain exhibits an optical bandgap of as high as 3.26 eV, and a highly efficient ultraviolet emission with peaks at 368 nm and 386 nm. An electroluminescence device from PDHFSCHD neat film as an active layer shows UV emission which peaks at 395 nm with a turn on voltage below 8 V By optimizing the device conditions, a peak EL quantum efficiency of 0.054% and brightness of 10 cd.m(-2) was obtained. Furthermore, blending a poly(dihexylfluorene) in the PDHFSCHD host gave pure blue emission peaking at 417 nm, and 440 nm without long wavelength emission from aggregated species. Efficient energy transfer from PDHFSCHD to PDHF was demonstrated in these blended systems. Depressed chain-aggregation of PDHF in the PDHFSCHD host can correspond to pure blue emission behaviors.

Synthesis and properties of PPP-based copolymers containing phenothiazine moiety

Novel soluble alternating conjugated copolymers (PFSP and PFSR) comprised of phenothiazine unit are synthesized by palladium-catalyzed Suzuki coupling reactions. Their thermal stability, photoluminescence, electroluminescence, hole injection and transport properties are investigated. The resulting copolymers exhibit good thermal stability and excellent hole-injection ability (about -5.2eV), which are closely matched to the work function of ITO. Double-layer devices demonstrate that PFSP is a promising hole-transporting material for electroluminescent devices.

Miscibility and crystallization behavior of poly(3-hydroxyvalerate-co-3-hydroxyvalerate)/poly(propylene carbonate) blends

Blends of synthetic poly(propylene carbonate) (PPC) with a natural bacterial copolymer of 3-hydroxybutyrate with 3-hydroxyvalerate (PHBV) containing 8 mol % 3-hydroxyvalerate units were prepared with a simple casting procedure. PPC was thermally stabilized by end-capping before use. The miscibility, morphology, and crystallization behavior of the blends were investigated by differential scanning calorimetry, polarized optical microscopy, wide-angle X-ray diffraction (WAXD), and small-angle Xray scattering (SAXS). PHBV/PPC blends showed weak miscibility in the melt, but the miscibility was very low. The effect of PPC on the crystallization of PHBV was evident. The addition of PPC decreased the rate of spherulite growth of PHBV, and with increasing PPC content in the PHBV/PPC blends, the PHBV spherulites became more and more open. However, the crystalline structure of PHBV did not change with increasing PPC in the PHBV/PPC blends, as shown from WAXD analysis. The long period obtained from SAXS showed a small increase with the addition of PPC.

Synthesis, characterization and fabrication on a glassy carbon electrode of a tetra-iron substituted sandwich-type pentadecatungstodiarsenate heteropolyanion

A novel sandwich-type compound, Na-12[Fe-4(H2O)(2)(As2W15O56)2].41H(2)O, has been synthesized. The compound was well-characterized by means of IR, UV-vis, W-183 NMR and elemental analyses. The compound crystallizes in the triclinic, P (1) over bar symmetry group. The structure of the compound is similar to that of Na-16[M-4(H2O)(2)(As2W15O56)(2)].nH(2)O (M = Cu, Zn, Co, Ni, Mn, Cd), and consists of an oxo-aqua tetranuclear iron core, [(Fe4O14)-O-III(H2O)(2)], sandwiched by two trivacant alpha-Wells-Dawson structural moieties, alpha-[As2W15O56]. Redoxelectrochemistry of the compound has been studied in buffer solutions at pH = 4.7 using polarography and cyclic voltammetry ( CV). The compound exhibited four one-electron couples associated with the Fe(III) center followed by three four-electron redox processes attributed to the tungsten-oxo framework. The compound-containing monolayer and multilayer films have been fabricated on a 4-aminobenzoic acid modified glassy carbon electrode surface by alternating deposition with a quaternized poly(4-vinylpyridine) partially complexed with [Os(bpy)(2)Cl](2+/-). CV, X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy and atomic force microscopy (AFM) have been used to characterize the multilayer films.