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31.
32.
含聚硅氧烷链双马来酰亚胺的合成与表征 总被引:8,自引:0,他引:8
合成了N-(4-羟基苯基)马来酰亚胺和含聚硅氧烷链双马来酰亚胺,并用FTIR、1HNMR、元素分析、GPC、DTA和TG对其进行了表征。 相似文献
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Colloidal forces between bitumen surfaces in aqueous solutions measured with atomic force microscope
Jianjun Liu Zhenghe Xu Jacob Masliyah 《Colloids and surfaces. A, Physicochemical and engineering aspects》2005,260(1-3):217-228
Colloidal forces between bitumen surfaces in aqueous solutions were measured with an atomic force microscope (AFM). The results showed a significant impact of solution pH, salinity, calcium and montmorillonite clay addition on both long-range (non-contact) and adhesion (pull-off) forces. Weaker long-range repulsive forces were observed under conditions of lower solution pH, higher salinity and higher calcium concentration. Lower solution pH, salinity and calcium concentration resulted in a stronger adhesion forces. The addition of montmorillonite clays increased long-range repulsive forces and decreased adhesion forces, particularly when co-added with calcium ions. The measured force profiles were fitted with extended DLVO theory to show the repulsive electrostatic double layer and attractive hydrophobic forces being the dominant components in the long-range forces between the bitumen surfaces. At a very short separation distance (less than 4–6 nm), a strong repulsion of steric origin was observed. The findings provide a fundamental understanding of bitumen emulsion stability and a mechanism of bitumen “aeration” in bitumen recovery processes from oil sands. 相似文献
35.
Jianjun ZhangFanzuo Kong 《Tetrahedron letters》2003,44(9):1839-1842
A general method for the synthesis of 2-xylose or glucuronic acid branched (1→3)-linked mannose oligosaccharides has been developed. As a typical example, the synthesis of the methyl glycoside of β-d-GlcpA-(1→2)-α-d-Manp-(1→3)-[β-d-Xylp-(1→2)-]α-d-Manp-(1→3)-[β-d-Xylp-(1→2)-]α-d-Manp, the repeating unit of the exopolysaccharide from Cryptococcus neoformans serovar A, was achieved in a regio- and stereoselective manner. 相似文献
36.
The phenomenon of enthalpy-entropy compensation in gas chromatography is examined. Using 53 probe solutes that span a wide range in size (dispersive interaction), dipolarity, hydrogen-bond-donor and hydrogen-bond-acceptor strength, enthalpy-entropy compensation is not observed, while for probe solutes within a homologous series enthalpy-entropy compensation is observed as predicted by the linear salvation energy relationship methodology. 相似文献
37.
[reaction: see text] Methodology for the stereoselective preparation of both (E)- and (Z)-alpha-fluoro-alpha,beta-unsaturated esters is described. 1-Bromo-1-fluoroalkenes (E/Z approximate 1:1) can be isomerized to high E/Z ratio mixtures, which participate in palladium-catalyzed carboalkoxylation and lead to (Z)-alpha-fluoro-alpha,beta-unsaturated esters in high stereoselectivity. The same starting material can also be kinetically reduced to get an E/Z ratio of 0:100; similar carboalkoxylation reaction at 70 degrees C affords (E)-alpha-fluoro-alpha,beta-unsaturated esters stereospecifically. 相似文献
38.
Jianjun Xu 《Journal of fluorine chemistry》2004,125(5):725-730
High E/Z ratio (E/Z>75:25) 1-bromo-1-fluorostyrenes, which were prepared by isomerization of 1-bromo-1-fluorostyrenes (E/Z≈1:1), underwent the Heck reaction with methyl acrylate, and (2E, 4Z)-methyl 5-aryl-4-fluoropenta-2,4-dienoates were successfully isolated. Heck reactions of (Z)-1-bromo-1-fluorostyrenes also occur. However, the products are difficult to separate in a pure form, since they have an obvious tendency to isomerize on a silica gel column. 相似文献
39.
本文以二茂镍为母体化合物,以氧化铝和氧化硅为担体制备了担载镍催化剂。为了表征其结构特点,对这些催化剂热分解处理前后的样品在日本筑波高能物理研究所(Photon-Factory)的同步辐射加速器BL—10B EXAFS实验站进行了外延x-光精细结构谱测定(透射法)。以单散射球面波理论对实验结果进行了多参数拟合,同时对母体化合物也进行了平行测定和拟合,以验证数据及拟合方法的可靠性。研究结果表明,母体化合物的EXAFS结果与文献XRD相一致;母体化合物与担体表面发生了强烈的化学作用;镍组分在催化剂表面高度分散,氧化铝与Ni(C_5H_5)_2有更强的相互作用形成。Ni[(O)_s]_n(n≈4),近一半的镍原子周围有0.30 nm处的镍原子散射;氧化硅上除Ni[(CO)_s]_n(n≈3)外,在0.30 nm处有配位数为2的非成键Ni原子。 相似文献
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