Synthesis of novel functional polyolefin containing carboxylic acid via Friedel-Crafts acylation reaction

The strong polar group, carboxylic acid, has triumphantly been introduced into ethylene and allylbenzene copolymers without obvious degradation or crosslinking via Friedel-Crafts (F-C) acylation reaction with glutaric anhydride (GA), succinic anhydride (SA) and phthalic anhydride (PA) in the presence of anhydrous aluminum chloride in carbon disulfide. Some important reaction parameters were examined in order to optimize the acylation process. In the optimum reaction conditions, almost all of the phenyls can be acylated with any anhydride. The microstructure of acylated copolymer was characterized by Fr-IR, H-1 NMR and H-1-H-1 COSY. All the peaks of acylated copolymers can be accurately attributed, which indicates that all the acylation reactions occur only at the para-positions of the substituent of the aromatic rings. The thermal behavior was studied by differential scanning calorimetry (DSC), showing that the melting temperatures (T(m)s) of acylated copolymers with GA firstly decrease slowly and then increase significantly with the increase of the amount of carboxyl acid groups.

High laser-induced damage threshold HfO2 films prepared by ion-assisted electron beam evaporation

HfO2 films were deposited by electron beam evaporation with different deposition parameters. The properties such as refractive index, weak absorption, and laser induced damage thresholds (LIDTs) of these films have been investigated. It was found that when pulsed Nd:YAG 1064 nm laser is used to investigate LIDT of films: Metallic character is the main factor that influences LIDTs of films obtained from Hf starting material by ion-assisted reaction, and films prepared with higher momentum transfer parameter P have fewer metallic character; The ion-assisted reaction parameters are key points for preparing high LIDT films and if the parameters are chose properly, high LIDT films can be obtained. (c) 2004 Elsevier B.V. All rights reserved.

One-pot synthesis and self-assembly of colloidal copper(I) sulfide nanocrystals

A simple one-pot method is developed to prepare size-and shape-controlled copper(I) sulfide (Cu2S) nanocrystals by thermolysis of a mixed solution of copper acetylacetonate, dodecanethiol and oleylamine at a relatively high temperature. The crystal structure, chemical composition and morphology of the as-obtained products are characterized by powder x-ray diffraction (PXRD), x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The morphology and size of the Cu2S nanocrystals can be easily controlled by adjusting the reaction parameters. The Cu2S nanocrystals evolve from spherical to disk-like with increasing reaction temperature. The spherical Cu2S nanocrystals have a high tendency to self-assemble into close-packed superlattice structures. The shape of the Cu2S nanodisks changes from cylinder to hexagonal prism with prolonged reaction time, accompanied by the diameter and thickness increasing. More interestingly, the nanodisks are inclined to self-assemble into face-to-face stacking chains with different lengths and orientations. This one-pot approach may extend to synthesis of other metal sulfide nanocrystals with different shapes and sizes.

Direct decomposition of NO activated by microwave discharge

The environmentally friendly removal of NO has been investigated using continuous microwave discharge (CMD) at atmospheric pressure. In these experiments, conversions of NO to N-2 as well as NO2 were mainly observed for both dry and wet feed gas, which showed a great difference from those observed with other discharge methods. The effects of a series of reaction parameters, including microwave input power, O-2 concentration, NO concentration, and gas flow rate, on the product distribution and energy efficiency were also studied. Under all reaction conditions, the conversions of NO to N-2 were higher than those to NO2. The highest conversion of NO to N-2 was 88%. The reaction rate of NO removal and the effects of the different discharge modes on NO conversion and product distribution are also discussed. Through comparison of the results of different discharge modes, it was found that the addition of CH4 apparently increased the conversion of NO to N-2 as well as the energy efficiency. A possible reaction process is suggested.

Direct decomposition of NO by microwave heating over Fe/NaZSM-5

Catalytic decomposition of NO was studied over Fe/NaZSM-5 catalyst. Novel results were observed with the microwave heating mode. The conversion of NO to N-2 increased remarkably with the increasing of Fe loading. The effects of a series of reaction parameters, including reaction temperature, O-2 concentration, NO concentration, gas flow rate and H2O addition, on the productivity of N-2 have been investigated. It is shown that the catalyst exhibited good endurance to excess O-2 in the microwave heating mode. Under all reaction conditions, NO converted predominantly to N-2. The highest conversion of NO to N-2 was up to 70%. (C) 2002 Elsevier Science B.V. All rights reserved.

Catalytic oxidation of cyclohexane over Ti-Zr-Co catalysts

Ti-Zr-Co alloys have been fabricated and characterized, and their catalytic performance was discussed for the oxidation of cyclohexane with oxygen under solvent-free condition. The icosahedral quasicrystalline phase (I-phase)-forming ability of Ti-Zr-Co alloys with different compositions was discussed, and it was confirmed that I-phase could be formed as a dominating phase at the Ti-rich composition region from Ti53Zr27Co20 to Ti75Zr5Co20 in as-cast alloys. The composition and microstructure of Ti-Zr-Co alloys present crucial influences on its catalytic activity and selectivity in the oxidation of cyclohexane. The influences of some reaction parameters such as temperature, reaction time, and catalyst amounts were also investigated. Ti70Zr10Co20 alloy containing quasicrystal microstructure showed good catalytic performance with a 6.8% conversion of cyclohexane and 90.4% selectivity of cyclohexanol and cyclohexanone. It behaves as an efficient heterogeneous catalyst for the oxidation of cyclohexane and could be recycled five times without loss in activity and selectivity.

Rectangular Silver Nanorods: Controlled Preparation, Liquid-Liquid Interface Assembly, and Application in Surface-Enhanced Raman Scattering

In this paper, we for the first time report a polyol method for large-scale synthesis of rectangular silver nanorods in the presence of directing agent and seeds. This method has some clear advantages including simplicity, high quality, and ease of scaleup. Silver nanowires or silver nanorods with a submicrometer diameter could also be facilely prepared when the reaction parameters are slightly changed. Furthermore, a liquid-liquid assembly strategy has been employed to construct uniform rectangular silver nanorod arrays on a solid substrate which could be used as surface-enhanced Raman scattering (SERS) substrates with high SERS activity, stability, and reproducibility. It is found that the SERS spectra obtained from the probe molecules with the different concentrations show different SERS intensifies. As the concentration of 4-aminothiophenol (4-ATP) or rhodamine 6G (R6G) increases, the SERS intensities progressively increase. The enhancement factor for 4-ATP and R6G should be as large as 5.06 x 10(4) or much larger than the value of 5.06 x 10(8), respectively.

(R,R)-DPEN-modified Ru/gamma-Al2O3 - An efficient heterogeneous catalyst for enantioselective hydrogenation of acetophenone

An efficient enantioselective catalyst of 5 wt.% Ru/-gamma-Al2O3 modified with R,R-1,2-diphenylethylene-diamine ((R,R)-DPEN) for the hydrogenation of a non-activated aromatic ketone of acetophenone has been investigated, a relatively high enantiomeric excess (ee) of 60.5% was obtained at both the conversion and selectivity larger than 99%, it was about three times higher than the ee values reported up to now for acetophenone hydrogenation with the supported transition metal catalysts modified by chiral reagents. The influences of some reaction parameters such as phosphine ligand, substrate/catalyst/modifier molar ratios, base, solvent, pressure and reaction temperature have been discussed. The chiral modifier of (R,R)-DPEN was very important in controlling the enantioselectivity through adsorption competing with other substrates on the surface of active metal species. The phosphine ligand and base were also important and indispensable in the present reaction.

Polymerization of methyl methacrylate by iron(II) pyridinebisimine complexes

Fe(II) pyridinebisimine complexes activated with trialkylaluminium or modified methylaluminoxane (MMAO) as catalysts were employed for the polymerization of methyl methacrylate. Polymer yields, activities and polymer molecular weights as well as molecular weight distributions can be controlled over a wide range by the variation of the structures of the Fe(II) pyridinebisimine complexes and the reaction parameters such as Al/Fe molar ratio, monomer/catalyst molar ratio, monomer concentration, reaction temperature and time applied to the polymerization of methyl methacrylate. Under optimum condition, the catalytic activity of Fe(II) complex is of up to 74.5 kg(polym)/mol(Fe)h.

Synthesis, structure and norbornene polymerization behavior of nickel complexes bearing two beta-ketoiminato chelate ligands

A series of nickel(II) complexes bearing two nonsymmetric bidentate beta-ketoiminato chelate ligands have been prepared, and the structures of complexes [(2,6-Me2C6H3)NC(CH3)C(H)C(Ph)O](2)Ni (4a) and [(2,6-Me2C6H3)NC(CH3)C(H)C(CF3)O](2)Ni (4c) have been confirmed by X-ray crystallographic analysis. These nickel(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 high molecular weight polymers. Catalytic activity of up to 1.16 x 10(4) kg/mol(Ni) .h and the viscosity-average molecular 9 weight of polymer of up to 870 kg/mol were observed. Catalyst activity, polymer yield, and polymer molecular weight could be controlled over a wide range by the variation of the reaction parameters such as Al/Ni molar ratio, norbornene/catalyst molar ratio, monomer concentration, polymerization reaction temperature and time.

Dispersion copolymerization of acrylamide with acrylic acid in an aqueous solution of ammonium sulfate: Synthesis and characterization

Dispersion copolymerization of acrylamide with acrylic acid in an aqueous solution of ammonium sulfate using poly(2-acrylamido-2-methylpropanesulfonic acid sodium) as the stabilizer and ammonium persulfate (APS) as the initiator was investigated. The influence of initiator concentration, stabilizer concentration, ammonium sulfate concentration, chain-transfer agent concentration, and polymerization temperature on the copolymerization was discussed. The results showed that varying the ammonium sulfate concentration could affect the particle size and the intrinsic viscosity of the copolymer significantly. With increasing the stabilizer concentration, the particle size of the copolymer decreased first, and then increased, meanwhile the intrinsic viscosity of the copolymer decreased. The increase of initiator concentration, chain-transfer agent concentration, and polymerization temperature resulted in the increase in the particle size. Polydisperse spherical particles were formed in the system, and the kinetics for the dispersion copolymerization were discussed.

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.

Spectroelectrochemical and voltammetric studies of L-DOPA

The electrooxidation of L-dopa at GC electrode was studied by in situ UV-vis spectroelectrochemistry (SEC) and cyclic voltammetry. The mechanism of electrooxidation and some reaction parameters were obtained. The results showed that the whole electrooxidation reaction of L-dopa at glassy carbon (GC) electrode was an irreversible electrochemical process followed by a chemical reaction in neutral solution (EC mechanism). The spectroelectrochemical data were treated by the double logarithm method together with nonlinear regression, from which the formal potential E-0 = 228 mV, the apparent electron-transfer number of the electrooxidation reaction an = 0.376 (R = 0.99, SD = 0.26), the standard electrochemical rate constant k(0) (3.93 +/- 0.12) x 10(-)4 cm s(-1) (SD = 1.02 x 10(-2)), and the formation equilibrium constant of the following chemical reaction k(c)= (5.38+/-0.34) x 10(-1) s(-1) (SD = 1.02 x 10(-2)) were also obtained.