Syntheses of chromium(III) complexes with Schiff-base ligands and their catalytic behaviors for ethylene polymerization

A series of chromium(III) complexes LCrCl3 (4a-c) bearing chelating 2,2'-iminodiphenyisulfide ligands [L = (2-ArMeC=NAr)(2)S] was synthesized in good yields from the corresponding ligands and CrCl3.(THF). Using modified methylaluminoxane (MMAO) as a cocatalyst, these complexes display moderate activities towards ethylene polymerization, and produce highly linear polyethylenes with broad molecular weight distribution. Polymer yields, catalyst activities and the molecular weights, as well as the molecular weight distributions of the polymers can be controlled over a wide range by the variation of the structures of the chromium(III) complexes and the polymerization parameters, such as Al/Cr molar ratio, reaction temperature and ethylene pressure.

Deformation mechanism of polystyrene toughened with sub-micrometer monodisperse rubber particles

Core-shell polybutadiene-graft-polystyrene (PB-g-PS) rubber particles with different ratios of polybutadiene to polystyrene were prepared by emulsion polymerization through grafting styrene onto polybutadiene latex. The weight ratio of polybutadiene to polystyrene ranged from 50/50 to 90/10. These core-shell rubber particles were then blended with polystyrene to prepare PS/PB-g-PS blends with a constant rubber content of 20 wt%. PB-g-PS particles with a lower PB/PS ratio (<= 570/30) form a homogeneous dispersion in the polystyrene matrix, and the Izod notched impact strength of these blends is higher than that of commercial high-impact polystyrene (HIPS). It is generally accepted that polystyrene can only be toughened effectively by 1-3 mu m rubber particles through a toughening mechanism of multiple crazings. However, the experimental results show that polystyrene can actually be toughened by monodisperse sub-micrometer rubber particles. Scanning electron micrographs of the fracture surface and stress-whitening zone of blends with a PB/PS ratio of 70/30 in PB-g-PS copolymer reveal a novel toughening mechanism of modified polystyrene, which may be shear yielding of the matrix, promoted by cavitation.

Synthesis and catalytic kinetics of tellurium-modified hyaluronic acid with glutathione peroxidase activity

A novel mimic TeHA was synthesized by modifying hyaluronic acid (HA) with tellurium, whose function is similar to that of glutathione peroxidase (GPX). The structure of TeHA was characterized by means of infrared spectroscopy and nuclear magnetic resonance spectroscopy, showing that the target Te is located at -CH2OH of the N-acetyl-D-glucosamine of HA. The activity of TeHA is 163.6 U/mu mol according to Wilson's method. In contrast to other mimics, TeHA displays a high activity. Moreover, TeHA can use many hydroperoxides as substrates, such as H2O2, cumenyl hydroperoxide, and tert-butyl hydroperoxide, and cumenyl hydroperoxide is the optimal substrate. A ping-pong mechanism was deduced for the reduction reactions catalyzed by TeHA according to the steady-state kinetic studies.

Electrochemical detection of DNA immobilized on gold colloid particles modified self-assembled monolayer electrode with silver nanoparticle label

The target DNA was immobilized successfully on gold colloid particles associated with a cysteamine monolayer on gold electrode surface. Self-assembly of colloidal An onto a cysteamine modified gold electrode can enlarge the electrode surface area and enhance greatly the amount of immobilized single stranded DNA (ssDNA). The electrontransfer processes of [Fe(CN)(6)](4)-/[Fe(CN)(6)](3-) on the gold surface were blocked due to the procedures of the target DNA immobilization, which was investigated by impedance spectroscopy. Then single stranded target DNA immobilized on the gold electrode hybridized with the silver nanoparticle-oligonucleotide DNA probe, followed by the release of the silver metal atoms anchored on the hybrids by oxidative metal dissolution, and the indirect determination of the released solubilized Ag-1 ions by anodic stripping voltammetry (ASV) at a carbon fiber microelectrode. The results show that this method has good correlation for DNA detection in the range of 10-800 pmol/1 and allows the detection level as low as 5 pmol/1 of the target oligonucleotides.

Luminescence and energy transfer of organically modified silica xerogels (OMSX) doped and undoped with Eu3+ and Tb3+

Organically modified silica xerogels (OMSX) and Eu3+ (Tb3+)-doped OMSX were prepared by the reaction of (3-aminopropyl) triethoxysilane (APS) with 3-isocyanatepropyltriethoxysilane (ICPTES) followed by the subsequent hydrolysis and condensation in the presence of Eu3+ (Tb3+) via sol-gel method, which were characterized by FT-IR, XRD, fluorescence excitation and emission spectra. The as-formed OMSX shows a strong blue emission with the maximum excitation and emission wavelength at 351 and 420 nm, respectively. Due to the spectral overlap between the emission band of OMSX and f-f absorption lines of Eu3+ and Tb3+ in the UV-blue region, an energy transfer was observed from OMSX host to Eu3+ and Tb3+ in OMSX/Eu3+ and OMSX/Tb3+, respectively. Excitation at 350-360 nm resulted in a very weak emission around 420 nm from OMSX host and strong emission of Eu3+ and Tb3+ in OMSX/Eu3+ and OMSX/Tb3+, respectively. The emission spectra of Eu3+ and Tb3+ consist of D-5(0)-F-7(J) (J = 0, 1, 2, 3, 4) and D-5(4)-F-7(J) (J = 6, 5, 4, 3), respectively. Furthermore, the predicted structure of OMSX/Eu3+ and OMSX/Tb3+ is presented.

AFM study of the self-assembly behavior of hexa-armed star polymers with a discotic triphenylene core

The size-armed polystyrenes and poly-(methyl methacrylate)s with a triphenylene core showed different self-assembling patterns, isolated cylinders for polySt on mico and highly ordered cylindrical pores for polyMMA on a silicon water. With a decrease of polymer concentration in tetrahydrofuran (HHF), the size and height of cylinders decreased for polySt, but fur polyMMA, the size and depth of the cylindrical pores increased. Slow evaporation of the solvent and a low molecular weight favored the formation of regular patterns.

Determination of molecular weight and molecular sizes of polymers by high temperature gel permeation chromatography with a static and dynamic laser light scattering detector

Flow-mode static and dynamic laser light scattering (SLS/DLS) studies of polymers, including polystyrene, polyethylene, polypropylene and poly(dimethylsiloxane) (PDMS), in 1,2,4-trichlorobenzene (TCB) at 150 degreesC were performed on a high temperature gel permeation chromatography (GPC) coupled with a SLS/DLS detector. Both absolute molecular weight (M) and molecular sizes (radius of gyration, R-g and hydrodynamic radius, R-h) of polymers eluting from the GPC columns were obtained simultaneously. The conformation of different polymers in TCB at 150 degreesC were discussed according to the scaling relationships between R-g, R-h and M and the rho-ratio (p = R-g/R-h). Flow-mode DLS results of PDMS were verified by batch-mode DLS study of the same sample. The presented technique was proved to be a convenient and quick method to study the shape and conformation of polymers in solution at high temperature. However, the flow-mode DLS was only applicable for high molecular weight polymers with a higher refractive index increment such as PDMS.

Preparation and luminescence properties of the mesoporous MCM-41s intercalated with rare earth complex

Rare earth complex Eu(DBM)(3)phen (DBM: dibenzoylmethane, phen: 1.10-phenanthroline) hits been incorporated into unmodified MCM-41 and modified MCM-41s by aminopropyltriethoxysilane (APTES) or N-[(3-triethoxysilyl)propyl]ethylenediamine(TEPED). Thus, the assemblies of unmodified or modified MCM-41s with rare earth (RE) complex have been obtained. XRD spectra. NMR spectra. diffuse reflectance spectra. and the luminescence spectra were used to characterize the pure RE complex and the corresponding assemblies. The assemblies have better luminescence properties under UV irradiation. and their fluorescence lifetimes on the excited state are longer than that of the corresponding pure complex. The possible mechanisms are also discussed in the context.

Design, synthesis and characterization of novel nitrogen-and sulfur-containing polymers with well-defined conjugated length

A series of novel nitrogen- and sulfur-containing conjugated polymers with well-defined conjugation length have been synthesized via an acid-induced self-polycondensation of functional monomers with methylsulfinyl groups. Synthesized polymers exhibit good solubility in common solvents, such as CHCl3, THF, DMF, DMSO, and NMP. With increased numbers of aminophenyl groups, these polymers have shown similar electrical properties to polyaniline (PAn), and these are demonstrated by UV-vis spectroscopy and cyclic voltammetry (CV) measurements on the polymers. The conductivity of preliminarily protonic-doped poly[phenylene sulfide-alt-tetrakis(aniline)] (PPSTEA) is up to 10(-1) S cm(-1).

Two new coordination polymers of Co(II) with 1,1 '-(1,4-butanediyl)bis(benzimidazole)

Two new compounds, [CoL2(H2O)(2)](NO3)(2). 8H(2)O (1) and [CoL(H2O)(2)(CH3CO2)(2)]. H2O (2), were obtained from self-assembly of the corresponding metal salts with 1,1'-(1,4-butanediyl)bis(benzimidazole) (L). In 1, each cobalt ion is coordinated to four nitrogen atoms from four molecules of L, and to two water molecules. Metal ions are bridged by L ligands to form infinite (4, 4) networks that contain 44-membered rings. The (4, 4) networks of 1 stack in a parallel fashion, resulting in the formation of large channels in the material. In 2, each cobalt ion is coordinated to two N atoms from two L molecules, two water molecules and two carboxylate O atoms from two acetate anions. Each L molecule is coordinated to two cobalt ions, acting as a bridging ligand as in 1. The bridged cobalt ions form an infinite zigzag chain structure.

Networks with hexagonal circuits in co-ordination polymers of metal ions (Zn-II, Cd-II) with 1,1 '-(1,4-butanediyl)bis(imidazole)

Three new compounds, [ZnL1.5(H2O)(SO4)]. 6H(2)O 1, [ZnL1.5(H2O)(2)][NO3](2). 2H(2)O 2 and [CdL1.5(H2O)(2)(SO4)]. 4H(2)O 3 were obtained from self-assembly of the corresponding metal salts with 1,1'-(1,4-butanediyl)bis(imidazole) (L). In both 1 and 2 zinc ion is five-co-ordinated, showing a less-common trigonal bipyramidal co-ordination polyhedron, while cadmium ion of 3 is six-co-ordinated with a common octahedral arrangement. The sulfate ions of 1 and 3 are co-ordinated, however the nitrate ions of 2 are not. Each of the three compounds is composed of a (6, 3) network with the hexagonal smallest circuit containing six metal ions and six L; each L is co-ordinated to two metal ions, acting as a bridging ligand. In 1 the 2-D sheet of (6, 3) networks is interpenetrated in an inclined mode by symmetry related, identical sheets to give an interlocked 3-D structure, while the (6, 3) networks of both 2 and 3 stack in a parallel fashion to construct frameworks having channels.

A hydrogen peroxide biosensor combined HRP doped polypyrrole with ferrocene modified sol-gel derived composite carbon electrode

A novel amperometric biosensor for the detection of hydrogen peroxide is described. The biosensor was constructed by electrodepositing HRP/PPy membrane on the surface of ferrocenecarboxylic acid mediated sol-gel derived composite carbon electrode. The biosensor gives response to hydrogen peroxide in a few seconds with detection limit of 5x10(-7) mol (.) L-1 (based on signal : noise=3). Linear range is up to 0.2 mmol (.) L-1.

Capacitive detection of glucose using molecularly imprinted polymers

A novel glucose biosensor based on capacitive detection has been developed using molecularly imprinted polymers. The sensitive layer was prepared by electropolymerization of o-phenylenediamine on a gold electrode in the presence of the template (glucose). Cyclic voltammetry and capacitive measurements monitored the process of electropolymerization. Surface uncovered areas were plugged with 1-dodecanethiol to make the layer dense, and the insulating properties of the layer were studied in the presence of redox couples. The template molecules and the nonbound thiol were removed from the modified electrode surface by washing with distilled water. A capacitance decrease could be obtained after injection of glucose. The electrode constructed similarly but with ascorbic acid or fructose only showed a small response compared with glucose. The stability and reproducibility of the biosensor were also investigated. (C) 2001 Elsevier Science B.V. All rights reserved.

Corona poling of liquid crystalline polymers with nitroazobenzene side chains

The orientational behavior of liquid crystalline polymers with para-nitro azobenzene as side chains under electric field was studied by UV-visible spectroscopy. The results showed that lambda(max) of the poled polymer films was around 394nm, compared to that of the unpoled films, the absorption decreased due to poling. The orientational parameters increased linearly with the increase of the electric field. The temporal stability of the poled polymer film is good at room temperature. This kind of materials showed promise application as nonlinear optical component in photorefractive polymers.