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961.
This paper describes several highly efficient aza-Baylis-Hillman reactions of N-tosylated imines with MVK, acrolein, and phenyl acrylate or alpha-naphthyl acrylate in the presence of a Lewis base. In most cases, the reaction can be completed within 1 h using the appropriate Lewis base catalyst. An efficient method to synthesize beta-amino ketones, aldehydes and esters in high yields and short reaction time has been developed. 相似文献
962.
Yuan L Feng W Yamato K Sanford AR Xu D Guo H Gong B 《Journal of the American Chemical Society》2004,126(36):11120-11121
Highly efficient, one-step macrocyclizations leading to the formation of macrocyclic hexa(aramides) in high yields (69-82%) are described. The one-step macrocyclizations were facilitated by the preorganization or folding of the backbones of uncyclized precursors in the course of macrocyclization. The preorganization of backbones was achieved by the presence of localized three-centered hydrogen bonds that were adopted in the design of a class of closely related, backbone-rigidified foldamers. The macrocyclization involved reactions between diacid chloride 1 and diamine 2. The crude reaction mixtures and products were conveniently examined by mass spectrometric method (MALDI-TOF). Compared to most traditional one-step macrocyclizations that usually require high dilution conditions and often lead to very low overall yields of the desired products, cyclic hexamers 3 were obtained as the overwhelmingly major product under a variety of reaction conditions, suggesting the generality of this approach. 相似文献
963.
Ultra-high-molecular-weight polyethylene (UHMWPE) – carbon black (CB) blends were prepared by gelation/ crystallization from
PE dilute solutions containing CB particles. The UHMWPE/CB composition chosen were 1/0.15, 1/0.25, 1/0.5, 1/0.75, 1/1, 1/3,
1/5, and 1/9, etc. The cross-linking of PE chains was performed by chemical reaction of dicumyl-peroxide at 160 °C. X-ray diffraction patterns indicate that the crystallinity of PE within the blends decreased drastically through the chemical
reaction at high temperature. The sample preparation method by gelation/crystallization provided the UHMWPE–CB system with
various CB contents up to 90% and the conductivities for the resultant specimens were in the range from 10-9 to 1 Ω-1 cm-1 corresponding to the electric conductivity range of semiconductors. The blends assured thermal stability of electric conductivity
by cross-linking of PE chains, although the mechanical property such as the storage and loss moduli were very sensitive to
temperature. The conductivity of the blends with CB content ≥20% were almost independent of temperature up to 220 °C and the values in the heating and cooling processes were almost the same. On the other hand, for the UHMWPE–CB blends with
13% CB content corresponding to the critical one, temperature dependence of electric resistivity showed positive temperature
coefficient (PTC) effect. The PTC intensities for non-cross-linked and cross-linked materials were lower than that of the
corresponding low-molecular-weight-polyethylene (LMWPE)–CB blend but the maximum peak appeared at 160 °C which is higher than the peak temperature of LMWPE–CB blend.
Received: 10 December 1997 Accepted: 9 April 1998 相似文献
964.
L. -M. Yuan R. -N. Fu S. -H. Gui X. -T. Xie R. -J. Dai X. -X. Chen Q. -H. Xu 《Chromatographia》1997,46(5-6):291-294
Summary The gas chromatographic separation of xylene isomers using special mixed stationary phases consisting of heptakis(2.3.6-tri-O-pentyl)-β-CD-AgNO3, heptakis (2.3.6-tri-O-pentyl)-β-CD-TINO3 or bentone-34-AgNO3 is investigated. The first two have positive synergistic effects for the separation of m, and p-xylene isomers, but negative
synergistic effects for the m, and oisomers. The separation effects depend on temperature, mixing ratio and how mixing is
accomplished. 相似文献
965.
966.
Kirsten Gesenberg Prashant P. Deshpande Annie Pullockaran Feng Xu Dedong Wu Qi Gao Charles Pathirana John Castoro Nachimuthu Soundararajan Andrew Staab 《Tetrahedron letters》2007,48(15):2675-2677
Transformation of 4,7-dimethoxy-6-azaindole into 4-hydroxy-7-methoxy-6-azaindole or 7-hydroxy-4-methoxy-6-azaindole can be readily controlled by careful selection of a reagent. Treatment with concentrated HCl results in hydrolysis at the 4-position exclusively, while TMS-I provides demethylation at the 7-position only. Products were unambiguously identified by single crystal X-ray crystallography. 相似文献
967.
968.
本文用三级相互作用近似理论导出了高分子链末端距的四次矩的计算公式。计算聚亚甲基链的末端距四次矩,并同二级相互作用的结果进行了比较。对于聚亚甲基链,三级相互作用近似的四次矩小于二级相互作用近似的四次矩。 相似文献
969.
多嵌段聚醚氨酯脲为基质的新型高分子固态离子导体 总被引:2,自引:0,他引:2
本文合成了一系列聚乙二醇型多嵌段聚醚氨酯脲,而且用这类聚醚氨酯甩与高氯酸锂制得了一种新型的高分子固态离子导体复合物。在室温和50℃之间,其电导率比聚环氧乙烷为基质的固体电解质的高一到二个数量级,它还具有优良的综合性能。因此,对于室温薄膜蓄电池来说,这种新型的固体电解质是一类良好的候选材料。 相似文献
970.
比较了H_4SiMo_(12)O_(40)、H_3PW_(12)O_(40)、H_4SiW_(12)O_(40)、H_3PMo_(12)O_(40)及铬酸盐对镀锌层钝化效果。H_3PMo_(12)O_(40)钝化的最佳条件为:H_3PMo_(12)O_(40)5g/L,pH 1.1,钝化时间35秒,温度15℃,空留时间10秒,封闭温度100℃(水)。经扫描电镜、XPS、AES、IR和Raman光谱等测定,表明在锌表面形成了一种含有P、Mo、O及Zn的耐蚀性膜。其中钼以Mo(Ⅵ)、Mo(Ⅴ)和Mo(Ⅳ)存在,P/Mo比为1:3.0。推测锌表面形成了一种形如Zn_x(PMo_3)_rO_z/ZnO/Zn的复杂钝化膜。 相似文献