钯催化Suzuki偶联反应的研究进展

金属Pd催化的Suzuki偶联反应是碳-碳偶联反应中重要的反应之一。综述了近年来Pd催化Suzuki偶联反应的研究进展,其中包括Suzuki反应机理、配体种类及其在有机合成中的应用。介绍了含N、P配体的钯催化剂和碳纳米管、磁性材料、多孔材料、水滑石、金属氧化物、高分子材料等负载的无配体钯催化剂的研究进展。     

Enantioselective Hydrogenation of (E)-α-phenylcinnamic Acid over Cinchonidine-modified Pd Catalysts Supported on TiO2 and CeO2

The effects of the catalyst support, reaction temperature, and concentration of the modifier were examined to optimize supported Pd-catalysts and reaction conditions for the achievement of higher enantiomeric excess in the hydrogenation of (E)-α-phenylcinnamic acid. Over 90% of enantioselectivity was achieved using a cinchonidine-modified 40 wt% Pd/TiO₂ catalyst at 288 K.     

Verbesserte Einsatzmöglichkeiten des 4-Methoxybenzylrestes als 2′-OH-Schutz bei Ribonucleotidsynthesen durch TFA-Acidolyse

An Improved Method for the Application of the 4-Methoxybenzyl Group to Protect the 2′-Hydroxyl Group in the Ribonucleotide Synthesis by TFA-acidolysis The cleavage of the 4-methoxybenzyl group from the 2′-OH-position of ribonucleosides by the hydrogenation with different Pd-catalysts as well as trifluoracetic acid has been studied in detail. During hydrogenation, side reactions at the base residue of cytidine-occurred which, however, could be extensively suppressed by PdCl₂ catalysis. More practicable results were obtained with trifluoracetic acid in the presence of cation scavengers, allowing smoothly to convert a series of 2′-methoxybenzyl ribonucleotides to the homogeneous deprotection products.     

A general integral method for the determination of empirical reaction rates and parameters

A general procedure for the determination of empirical rates and kinetic parameters of irreversible, constant volume reactions is presented which is clearly superior to the conventional methods of kinetic analysis. By nonlinear regression of the integrated potential rate equation for stoichiometrically independent reactions of n the order, the empirical pre-exponential factor, activation energy, and reaction order are obtained. The regression equation relates explicitly the final concentration of the reference component not only to the time parameter of the reaction but also to the initial concentration. This includes an integral method for the determination of reaction orders in concentration. Two limiting cases are treated - the stoichiometric mixture of reactants and a mixture with one reactant in large excess. By analysis of standard Hougen-Watson rate models the dependence of empirical reaction orders on experimental conditions and simulated rate parameters is evaluated. By grouping the data into ranges of monotonous concentration change, conversion rates and rate parameters of reactions with changing volumes are calculated in a less rigorous deduction. The simplified interpretation of published experimental data is demonstated for the total oxidation of methane on Pd-catalysts and the dehydrogenation of cyclohexanol on ZnO.     

Transition metal catalyzed polymerisation of norbornene

Summary Metallocene/methylaluminoxane and single component Pd(II)-catalysts are compared to methylaluminoxane activated Ni and Pd-catalysts for the vinylpolymerisation of norbornene. Ni(II), Ni(0) and Pd(II)-compounds were found to be orders of magnitude more active than metallocenes and produce polymers of much higher molecular weights. Polymerisation kinetics for these systems have been studied in detail and reflected high initial activity followed by significant catalyst deactivation. Based on NMR-spectroscopy and WAXS five types of polynorbornenes have been identified and structures are proposed. Received: 4 June 1998/Revised version: 28 July 1998/Accepted: 28 July 1998     

Investigations of Palladium Catalysts on Different Carbon Supports

Pd-catalysts (5 wt%) were prepared on various supports: powdered and pelletized activated carbon derived from pine wood or beech wood, carbon black, and graphitized carbon black. The supports were palladized in the original condition or after HCl-treatment. The catalysts were characterized with CO-chemisorption, transmission electron micrographs, and X-ray photoelectron spectrometry. The precious metal dispersion and the catalytic activity are improved by the acid treatment of activated carbon as well as carbon black supports. A selection of samples were also characterized by means of inelastic neutron scattering (INS) to study the hydrogen-related features of the acid modification of the carbon supports. Indications for different sensitivities of the final Pd/C-catalysts to catalytically driven hydrogasification effects of the supports and the impact of these effects on the precious metal dispersion and the formation of Pd-hydrides were obtained. The formation of molecular-like polyaromatic structures was observed especially on HCl-treated activated carbon due to enhanced spillover of active hydrogen from the Pd-particles to adjacent sites on the support. The generation and accessability of these sites on the support seems to be promoted by the removal of ash and adsorbed species.     

Unterschiede in der Totaloxidation organischer Verbindungen an heterogenen Platin- und Palladiumkatalysatoren

Differences in the Total Oxidation of Organic Compounds on Heterogeneous Pt- and Pd-Catalysts The catalytic oxidation of selected organic compounds was studied on supported Pd and Pt catalysts and on massive wires. Unfunctionalized (Decane), unsaturated (dodecene, benzene), oxygen containing (1-octanol, formaldehyde, acetone, n-butylacetate, formic acid), nitrogen containing (aniline, pyridine), sulfur containing (thiophene) and chlorinated (1,2-dichloroethane) hydrocarbons were used as model compounds. The relative activity of the metals for oxidation of the various compounds was determined from the turnover frequencies. While platinum is more active for the oxidation of the unfunctionalized, aromatic and chlorinated compounds, palladium is more active for nitrogen and sulfur containing compounds and for formic acid. No specificity is found for alkenes and compounds with a lower oxygen content. In the presence of octane, the unreactive pyridine is much more effectively oxidized than pyridine alone. There are distinct differences for the oxidation of octane/pyridine mixtures on bimetallic, mixed and pure Pt- and Pd-catalysts. The bimetallic catalyst and the pure Pt-catalyst dominate with respect to conversion and selectivity. The oxidation of linear alkanes on Pt correlates with the boiling point. Pd catalyzes the oxidation of lower hydrocarbons (< C₅) better, while higher hydrocarbons ( > C₅) are better oxidized by Pt.     

Structure and property characterization of spunbonded filaments and webs using thermal analysis

The thermal history and inherent properties of the filaments are of utmost importance in spunbonded webs. A good understanding of the structure and properties development of individual filaments is helpful in comprehending the whole process better. Polypropylene homopolymer and a copolymer were processed using the Reicofi® spunbonding line at the Textiles and Nonwovens Development Center of the University of Tennessee, Knoxville. The properties of the filament samples taken before thermal bonding were determined through a variety of thermal analyses, such as differential scanning calorimetry, thermomechanical analysis, thermal deformation analysis, and dynamic thermal analysis, as well as mechanical properties. The performance properties of the bonded nonwoven fabrics from these filaments were evaluated, and the structure and properties of the fibers were compared with those of the bonded fabrics. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 421–434, 1998     

有限元分析在塑料加工与制品性能分析中的应用

主要介绍了在加工方面利用有限元分析法对模具的结构、浇注系统和冷却系统进行合理的设计以及对挤出成型过程中挤出胀大现象的预测;在制件性能分析方面对制件的结构进行模拟,并结合制件结构特点对其力学性能、电学性能、热学性能等进行预测和分析.     

Mechanical,Thermal and Morphological Characterization of High-Density Polyethylene and Vermiculate Composites

High-density polyethylene composites containing 7, 10, 15 and 20% w/w vermiculite (VMT) were prepared by extrusion in a twin-screw extruder at various shear rates. The thermal and mechanical properties and morphological characteristics of the composites were evaluated and compared with pure high-density polyethylene. The blend morphologies were determined by scanning electron microscopy (SEM). The thermal properties of the composites were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The TGA results reveal that the use of VMT particles to fill polyethylene increased the thermal stability of the composite. The results obtained indicate that a shear speed of 400 rpm and vermiculite content of 7% showed the best properties of impact resistance. These observations were confirmed by morphology analysis.     

Biomass Thermogravimetric Analysis: Uncertainty Determination Methodology and Sampling Maps Generation

The objective of this study was to develop a methodology for the determination of the maximum sampling error and confidence intervals of thermal properties obtained from thermogravimetric analysis (TG), including moisture, volatile matter, fixed carbon and ash content. The sampling procedure of the TG analysis was of particular interest and was conducted with care. The results of the present study were compared to those of a prompt analysis, and a correlation between the mean values and maximum sampling errors of the methods were not observed. In general, low and acceptable levels of uncertainty and error were obtained, demonstrating that the properties evaluated by TG analysis were representative of the overall fuel composition. The accurate determination of the thermal properties of biomass with precise confidence intervals is of particular interest in energetic biomass applications.     

抗冲击共聚聚丙烯的结构与性能

对3种抗冲击共聚聚丙烯的力学性能进行了研究,并且采用动态力学分析、二甲苯溶出、溶胶凝胶渗透色谱和核磁共振等方法分析了抗冲共聚聚丙烯结构对其力学性能的影响。结果表明:提高共聚聚丙烯中乙丙橡胶相和聚丙烯基体之间的相容性,增加橡胶相含量,增大相对分子量并使其分布较窄,增加橡胶相中乙丙无规共聚物含量均有利于提高共聚聚丙烯的冲击强度。     

Mechanical and thermal properties of bisphenol A-based cyanate ester and diallyl phthalate blends

Cyanate ester resins are a high performance class of compounds. They have excellent mechanical properties, dielectric properties and thermal properties; however, their major drawback is their brittleness. An attempt was made to improve the impact strength of the cyanate ester resin. In the present study a commonly used cyanate resin, bisphenol A dicyanate (BADCy), was modified by the addition of diallyl phthalate (DAP) and was cured with benzoyl peroxide. The properties of the blends such as thermal and mechanical properties were investigated in detail by scanning electron microscope, dynamic mechanical analysis, thermogravimetric analysis, and mechanical measurement. The results indicate that the addition of the appropriate amount of DAP can effectively improve the impact toughness and the flexural strength while sacrificing the thermal properties of the blends. The maximum impact strength and flexural strength were observed on addition of 15 phr DAP content. However, the thermal stability of the blends was found to be lower than that of the unmodified BADCy resin.     

Synthesis and thermomechanical characterization of polyurethane elastomers extended with α,ω‐alkane diols

A series of polyurethane (PU) elastomers was prepared by the reaction of poly(?‐caprolactone) and 4,4′‐diphenylmethane diisocyanate, which was extended with a series of chain extenders (CEs) having 2–10 methylene units in their structure. The completion of the reaction was confirmed by Fourier transform infrared spectroscopy. The chemical structures of the synthesized PU samples were characterized with Fourier transform infrared, ¹H‐NMR, and ¹³C‐NMR spectroscopy, and the thermal properties were determined by thermogravimetric analysis, DSC, and dynamic mechanical thermal analysis techniques. The mechanical properties were also studied and are discussed. The thermogravimetric analysis and DSC analysis showed that CE length had a considerable effect on the thermal properties of the prepared samples. The dynamic mechanical thermal analysis and damping peaks were also affected by the number of methylene units in the CE length. The elastomer extended with 1,2‐ethane diol exhibited optimum thermal properties, whereas the elastomer based on 1,10‐decane diol displayed the worst thermal properties. Tensile strength and elongation at break decreased with increasing CE length, whereas hardness showed the opposite trend. The glass‐transition temperature moved toward lower temperatures with increasing CE length. The decrease in the glass‐transition temperature and tensile properties were interpreted in terms of decreasing hard segments and increasing chain flexibility. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characterization of polyurethane coatings derived from polyols synthesized with glycerol, phthalic anhydride and oleic acid

Polyester polyols, with various oleic acid contents were used in the preparation of polyurethane (PUR) coatings. The polyols were designated as Alk28, Alk40 and Alk65, in which 28, 40 and 65 represents the percentages of oleic acid in the respective formulations. The physical properties of the polyols such as acid value and hydroxyl value have been determined and the infrared (IR) spectroscopic analysis of the polyols is reported. The polyols were reacted with aromatic isocyanate (toluene 2,4-diisocyanate, TDI) to form PUR coatings. The effects of varied NCO/OH ratio and oleic acid content of polyols on physical properties of PUR coatings on mild steel panel were determined. The characterization of PUR coatings carried out by IR spectroscopic analysis and physico-chemical properties such as drying time, pencil hardness, adhesion properties, solvent resistance and corrosion/chemical resistant determination were reported. The coatings obtained from polyol Alk28, exhibits the best overall properties followed by Alk40. PUR coatings from Alk65 were softer. As the NCO/OH ratio of the coatings increased, there were progressive increases in mechanical and anticorrosive properties for all the coatings. Overall, these studies showed that the material holds promise for use as effective surface coating compound by designing the formulation of the desired performance.     

Esterification of Galactomannan and Polyacid as Paper Strengthening Agent

In this paper, eight paper strengthening agents were obtained by the esterification of galactomannan with trimesic acid or butanetetracarboxylic acid. The esterified galactomannan was studied using a ¹³C NMR spectrum, Frontier transform infrared spectroscopy, and elemental analysis. Then, the properties of the paper with esterified galactomannan were also investigated. The results of the ¹³C NMR spectrum and infrared spectroscopic analysis showed that the galactomannan had been successfully esterified with the trimesic acid or butanetetracarboxylic acid. The paper properties with 1% esterified galactomannan were found to be efficiently improved, when compared with the control sample. The polyacid dosages were also found to affect the paper properties. The SEM analysis showed that the esterified galactomannan could effectively increase the inter-fiber bonding in the paper.     

Synthesis and characterization of polyurethane coatings derived from polyols synthesized with glycerol,phthalic anhydride and oleic acid

Polyester polyols, with various oleic acid contents were used in the preparation of polyurethane (PUR) coatings. The polyols were designated as Alk28, Alk40 and Alk65, in which 28, 40 and 65 represents the percentages of oleic acid in the respective formulations. The physical properties of the polyols such as acid value and hydroxyl value have been determined and the infrared (IR) spectroscopic analysis of the polyols is reported. The polyols were reacted with aromatic isocyanate (toluene 2,4-diisocyanate, TDI) to form PUR coatings. The effects of varied NCO/OH ratio and oleic acid content of polyols on physical properties of PUR coatings on mild steel panel were determined. The characterization of PUR coatings carried out by IR spectroscopic analysis and physico-chemical properties such as drying time, pencil hardness, adhesion properties, solvent resistance and corrosion/chemical resistant determination were reported. The coatings obtained from polyol Alk28, exhibits the best overall properties followed by Alk40. PUR coatings from Alk65 were softer. As the NCO/OH ratio of the coatings increased, there were progressive increases in mechanical and anticorrosive properties for all the coatings. Overall, these studies showed that the material holds promise for use as effective surface coating compound by designing the formulation of the desired performance.     

Synthesis of flame retardant polyester‐urethanes and their applications in nanoclay composites and coatings

This paper describes the synthesis of phosphorus‐containing polyester‐urethanes and their applications in nanoclay composites and coatings. Polyester was prepared by the reaction of bis(bisphenol‐A) monophenyl phosphonate, maleic anhydride and phthalic anhydride. The polyester was reacted with various diols such as ethylene glycol, diethylene glycol and propylene glycol to obtain polyester polyols. Synthesized polyester polyols were characterized by chemical analysis and instrumental analysis and was used further to react with different isocyanates to develop polyester‐urethanes. The synthesized polyester‐urethanes were blended with organo‐modified montmorillonite nanoclay (1 wt%, 3 wt% and 5 wt%) and were cast in a mold and coated on mild steel panels. The thermal stability of neat polyester‐urethane and the nanoclay composites was determined by thermogravimetric analysis. The flame retardant properties of cast films and their composites were determined by the limiting oxygen index and UL‐94 test methods. The physical and mechanical properties of coatings such as pot life, drying properties, scratch hardness, pencil hardness, impact resistance, adhesion and flexibility were investigated. The chemical resistance properties of the coatings were also determined in different reagents. The data reveal that the polyester‐urethane nanoclay composites with 3 wt% clay hold promise for use in effective flame retardant coatings. © 2013 Society of Chemical Industry     

Mechanical,thermal, and morphological properties of bismaleimide/unsaturated polyester copolymers

An unsaturated polyester (UP) resin was modified by the addition of a thermosetting bismaleimide (BMD) as a second coreactive monomer. The copolymers were characterized in terms of mechanical, thermal, and morphological properties by tensile, bend, and impact testing; thermogravimetric analysis; heat deforming temperature analysis; dynamic mechanical analysis; and scanning electron microscopy. In addition, Fourier transform infrared spectroscopy of modified resin indicated that crosslinking networks were formed between BMD and UP. The properties of the modified resins were compared with those of unmodified resins. The results indicate that the addition of BMD not only improved the thermal decomposition temperature and heat deforming temperature but also caused small changes in the mechanical properties. The effect of the construct of BMD and the reactions among BMD, UP, and styrene were analyzed. The results show that BMD has great potential to improve the properties of UP. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 593–598, 2006     

海南火山岩结构及性能的研究

海南火山岩的物质组成和物理化学性能是评价其质量、物理化学活性和预测工业应用状况的重要依据.为了确认工业应用前景和进行合理开发利用,本文利用TG-DSC、XRD、SEM及化学全分析等分析方法对海南火山岩样品进行了高温特性、物相组成、微区形貌以及化学成分等分析.结果表明,样品具有良好的理化性能.通过化学成分分析表明,SiO...