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71.
Donna M. Brestensky Thomas R. Hoye Christopher W. Macosko 《Journal of polymer science. Part A, Polymer chemistry》1995,33(12):1957-1967
Anionic living polymerization methods, using organometallic initiators such as butyllithium reagents, have proven useful for, inter alia, styrene polymerization and are amenable to subsequent functionalization of poly(styryl)lithium in the termination step. In this study, general methods for the selective preparation of small styrene oligomers and termination of the intermediate oligo(styryl)lithium anions were investigated. The crude reaction mixtures were analyzed directly by tandem gas chromatography/mass spectrometry (GC/MS). Of the carbon- and silicon-based electrophiles tested, chloro(chloroalkyl)silanes, Cl-SiR2(CH2)nCl in particular, were shown by GC/MS to be regioselective end-capping reagents, thus allowing subsequent transformation to the primary amine. The combined GC/MS data allow not only an estimate of the degree of functionalization, but also the identification of by-products, thus providing insight into the end-capping process that otherwise might be difficult to access. © 1995 John Wiley & Sons, Inc. 相似文献
72.
O. N. Leonidova V. I. Voronin I. A. Leonidov R. F. Samigullina B. V. Slobodin 《Journal of Structural Chemistry》2003,44(2):243-247
The crystal structures of vanadates Li1-2xCo1+xVO4 with x = 0 and 0.25 have been studied by a full pattern analysis. It has been shown that in cubic spinel LiCoVO4 (space group Fd3m), the 8a tetrahedral sites contain a majority of vanadium and a small amount of lithium; all cobalt, lithium, and a small amount of vanadium occupy the 16d octahedral sites. Li0.5Co1.25VO4 crystals belong to the rhombic system (Imma space group) with unit cell parameters a = 5.939(1), b = 5.810(1), and c = 8.303(1). On substitution of lithium by cobalt according to the scheme 2Li+ Co2+ + , half of the lithium and 70% of the vacancies formed are in the 4a octahedral sites, and onethird of lithium and most of cobalt occupy the 4d octahedral sites. The 4e tetrahedral sites are completely occupied by vanadium and lithium in a ratio of 0.92/0.08. The interatomic distances in LiCoVO4 and Li0.5Co1.25VO4 are calculated, and the sizes of lithium ion transport channels are evaluated. 相似文献
73.
Alessandra LattanziLiliana R. Orelli Patrizia BaroneAntonio Massa Patrizia IanneceArrigo Scettri 《Tetrahedron letters》2003,44(7):1333-1337
A mild and practical procedure of Horner-Wadsworth-Emmons olefination promoted by lithium hydroxide and α-cyano phosphonates has been set up for the synthesis of α,β-unsaturated nitriles. The reaction conditions are tolerated by functionalized ketones and the exclusive formation of E-γ-hydroxy α,β-unsaturated nitriles has been observed. 相似文献
74.
Perovskite-type barium lithium fluoride (BaLiF3) was synthesized by pyrolysis of metal trifluoroacetates. The reaction temperature necessary for producing a single-phase material was found to be 600°C, which was lower than that for a conventional solid-state reaction or a melting method. Eu-doped BaLiF3 was also prepared and characterized to examine the suitability of trifluoroacetates for precursors in synthesizing homogeneous complex metal fluoride materials. It was demonstrated that trivalent Eu3+, which was used as acetate for a starting material, was reduced to divalent Eu2+ in the pyrolysis process of BaLiF3, as indicated by a broad blue emission due to an allowed 4f65d→4f7 transition at 408 nm with a ultraviolet excitation at 254 nm. The concentration quenching of the blue emission occurred at 5 at% of Eu in BaLiF3, indicating that Eu was homogeneously dispersed in the BaLiF3 host lattice. Mechanisms of the formation and reduction process of BaLiF3 were discussed based on pertinent chemical reactions. 相似文献
75.
锂离子二次电池电解质材料LiPF6的制备及表征 总被引:3,自引:0,他引:3
0引言 液态锂离子电池自1990年开发成功以来,由于具有比能量高、工作电压高、应用温度范围宽、自放电率低、循环寿命长、无污染、安全性能好等许多独特的优势[1],所以其发展前景十分广阔.目前液态锂离子二次电池中开发使用的无机阴离子导电盐主要有LiClO4、LiPF6、LiAsF6等,但LiClO4为强氧化剂,使用不安全而不宜用于电池,LiAsF6虽然性能颇佳,但有毒且价格较贵,故也不宜广泛使用.LiPF6被认为是目前较合适的电解质[1],但其制备困难,价格较贵,且目前报道的合成方法也多是以HF为介质[2~5].本文作者以PF5和LiF为原料在CH3CN溶剂中简单有效地合成了高纯LiPF6,并通过在手套箱中制样的方法对目标产物进行了红外、热重和X射线衍射分析,给出了LiPF6的红外光谱图、热重分析数据和X射线衍射图. 相似文献
76.
Fluorine-doped nanocrystalline tin dioxide materials (F:SnO2) have been successfully prepared by the sol-gel process from a single molecular precursor followed by a thermal treatment at 450-650 °C. The resulting materials were characterized by FTIR spectroscopy, powder X-ray diffraction, nitrogen adsorption porosimetry (BET) and transmission electron microscopy (TEM). The mean particle size increased from 5 to 20 nm and the specific surface area decreased from 123 to 37 m2/g as the temperature of heat treatment was risen from 450 to 650 °C. Fluorine-doped nanocrystalline SnO2 exhibited capacity of 560, 502, and 702 mA h/g with 48%, 50%, and 40% capacity retention after 25 cycles between 1.2 V and 50 mV at the rate of 25 mA/g, respectively. In comparison, commercial SnO2 showed an initial capacity of 388 mA h/g, with only 23% capacity retention after 25 cycles. 相似文献
77.
催化活性测试表明,助剂Fe具有显著提高乙醇生成选择性及铑催化活性的双重作用;助剂Li具有显著提高乙醇选择性的作用,对铑催化活性影响不大。基于H_2/D_2同位素效应结果及CO化学吸附、IR、XRD、XPS等的表征结果,认为助剂Fe经活化处理后大部分与Rh形成RhFe合金,使Rh分散度显著提高,从而提高了乙醇的选择性;Rh分散度的提高以及小部分以Fe~(2+)(Fe~(3+))形式存在的助剂Fe促进甲酰基的生成及随后的氢解断C-O键反应是助剂Fe促使铑催化活性提高的两个因素。Li的主要作用在于通过与C_2含氧中间体乙烯酮氧端的弱亲合作用,促进了乙醇前驱体的生成,从而使乙醇生成选择性提高。 相似文献
78.
Numerous carbonaceous materials have been studied as anodes of lithium ion batteries during the past several years[1 ̄4].Graphite was favored for battery applications because it exhibits a high specific capac- ity, low working potential close to that of l… 相似文献
79.
Graphitic anode materials for lithium ion batteries processed under high humidity conditions show severe performance losses. The sensitivity of these materials towards humidity can be significantly reduced by adsorbing metal ions like silver or copper ions, with subsequent heat treatment of these composites. Results of X-ray photoelectron spectroscopy, high-resolution electron microscopy, thermogravimetry, and differential thermal analysis indicate that the deposited metals exist in metallic and carbide, MxC (M=Cu or Ag), forms. They remove or cover (i.e. deactivate) active hydrophilic sites at the surface of the graphite. These composites absorb less water during processing. The electrochemical performance, including reversible capacity, coulombic efficiency in the first cycle, and cycling behavior, is markedly improved. This approach provides a potentially powerful method to manufacture lithium ion batteries under less demanding conditions.Presented at the 3rd International Meeting on Advanced Batteries and Accumulators, 16–20 June 2002, Brno, Czech Republic 相似文献
80.
总结了铌酸锂晶体的各项性能指标,显示了其对晶体实际组成的强烈依赖性.利用化学键模型定量地解释了这种依赖性产生的根源,从而说明了制约该晶体性能提高的关键因素是晶体结构中的缺陷控制. 相似文献