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971.
Wen Li Dalin Wu A. Dieter Schlüter Afang Zhang 《Journal of polymer science. Part A, Polymer chemistry》2009,47(23):6630-6640
An improved strategy to synthesize oligo(ethylene glycol)‐based secondary generation (G2) dendron is presented. The overall synthesis efficiency increased by 50% when comparing to the previous method, and the product purification by column chromatography becomes much easier. Based on this approach, the synthesis of the third‐generation (G3) dendrons and the corresponding methacrylate‐based G3 macromonomer becomes feasible. Because of the oil characteristics of this macromonomer, its polymerization was able to be conducted in bulk with AIBN as the initiator. The polymerization degree of the third‐generation dendronized polymer ( PG3 ) was found to be around 16 based on GPC measurement. The thermally induced dehydration processes of this polymer were monitored by temperature‐varied proton NMR spectroscopy, and its thermoresponsive behaviors were investigated with turbidity measurements using UV–vis spectroscopy. Similar to the lower generation counterparts, this threefold branched dendronized polymer also shows characteristic fast and sharp phase transitions around its apparent lower critical solution temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6630–6640, 2009 相似文献
972.
Tianfa Wen Jianping Gao Jiuming Zhang Beiya Bian Juyun Shen 《Infrared Physics & Technology》2001,42(6):241-508
A metallic (Ag)–dielectric (AgI) hollow glass waveguide is a promising and flexible fiber for the delivery of high-power CO2 laser radiation. The thickness of metallic (Ag) films and dielectric (AgI) films is a critical factor which greatly influences the attenuation of the waveguides. In this paper, metallic (Ag)–dielectric (AgI) films were successfully prepared in the capillary whose inner diameter is 0.53 mm, and firstly investigated with theoretical analysis and measured by means of AES and SEM. There is good agreement between theoretical thickness and experimental results, which confirms the validity of the theoretical analysis, which makes the estimate of the thickness of both the metallic and dielectric films possible with high accuracy prior to the preparation of hollow glass waveguides. The attenuation spectra of Ag/AgI hollow waveguides shows the loss increases with the thickness of Ag, AgI films and indicates that the Ag/AgI hollow waveguide is suitable for the transmission of IR radiation. 相似文献
973.
Liu Wen N. I. Sorokina V. I. Voronkova V. K. Yanovskii I. A. Verin A. G. Vigdorchik V. I. Simonov 《Crystallography Reports》2000,45(3):386-388
To reveal correlations between the atomic structure and properties of the KTi1-x SnxOPO4 solid solutions, single crystals of the KTi0.93Sn0.07OPO4 composition were synthesized and their structure was determined. The crystals belong to the KTiOPO4 family; orthorhombic, sp. gr. Pna21. The unit-cell parameters are a = 12.831, b = 6.410, and c = 10.584 Å. The partial substitution of Sn atoms for Ti atoms results in the formation of more symmetric coordination polyhedra in the structure framework and the change of the physical properties of the crystals. 相似文献
974.
令t(G)为有限阿贝尔群G的单因子个数.本文得到了∑|G|≤xt(G)带有更好余项的渐近公式. 相似文献
975.
Weiwei Zuo Shu Zhang Shaofeng Liu Xijie Liu Wen‐Hua Sun 《Journal of polymer science. Part A, Polymer chemistry》2008,46(10):3396-3410
6‐Benzimidazolylpyridyl‐2‐carboximidic half‐titanocene complexes, Cp′TiLCl (Cp′ = C5H5, MeC5H4, C5Me5, L = 6‐benzimidazolylpyridine‐2‐carboxylimidic, C1–C13 ), were synthesized and characterized along with single‐crystal X‐ray diffraction. The half‐titanocene chlorides containing substituted cyclopentadienyl groups, especially pentamethylcyclopentadienyl groups were more stable, while those without substituents on the cyclopentadienyl groups were easily transformed into their dimeric oxo‐bridged complexes, (CpTiL)2O ( C14 and C15 ). In the presence of excessive amounts of methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all half‐titanocene complexes showed high catalytic activities for ethylene polymerization. The substituents on the Cp groups affected the catalytic behaviors of the complexes significantly, with less substituents favoring increased activities and higher molecular weights of the resultant polyethylenes. Effects of reaction conditions on catalytic behaviors were systematically investigated with catalytic systems of mononuclear C1 and dimeric C14 . With C1 /MAO, large MAO amount significantly increases the catalytic activity, while the temperature only has a slight effect on the productivity. In the case of C14 /MAO catalytic system, temperature above 60 °C and Al/Ti value higher than 5000 were necessary to observe good catalytic activities. In both systems, higher reaction temperature and low cocatalyst amount gave the polyethylenes with higher molecular weights. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3396–3410, 2008 相似文献
976.
Jing Sun Jian‐Gong Cheng Wen‐Qing Zhu Shi‐Jie Ren Hong‐Liang Zhong Dan‐Li Zeng Jun‐Ping Du Er‐Jian Xu Ying‐Chun Liu Qiang Fang 《Journal of polymer science. Part A, Polymer chemistry》2008,46(16):5616-5625
A new X‐shaped π‐conjugated monomer comprising of fluorene units and anthracene units was synthesized, and it was used to fabricate the new X‐shaped π‐conjugated polymers and investigate the properties of the new polymers. Using different molar ratios between such monomer and a fluorene monomer gave three polymers that showed higher absolute PL quantum yields than the linear polyfluorene (PF) in the solid state. After thermal annealing at 200 °C for 4 h, the linear PF showed an additional bathochromic emission at about 550 nm, whereas such red‐shifted emission was fully eliminated for the X‐shaped polymers. The electroluminescent devices based on the X‐shaped polymers with a configuration of ITO/PEDOT:PSS/polymer/LiF/Ca/Al displayed blue emission with low turn‐on voltage and high brightness. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5616–5625, 2008 相似文献
977.
Guo Dong LIU Wen Peng ZHANG 《数学学报(英文版)》2008,24(2):343-352
The authors establish an explicit formula for the generalized Euler NumbersE2n^(x), and obtain some identities and congruences involving the higher'order Euler numbers, Stirling numbers, the central factorial numbers and the values of the Riemann zeta-function. 相似文献
978.
丙二酸酯衍生物2用2-氯硒基苯甲酰氯和2-(2-胺基乙氧基)乙醇为原料,经三步合成制得。2与C60的Bingel环加成反应制得C60基Ebselen衍生物3,产率为42% (基于已反应的C60),1HNMR、13CNMR、IR、FAB-MS和元素分析鉴定了其结构。为了证实3对鼠胸腺细胞的活力具有增强效应,C60衍生物4和2被选择,并采用与3相同的方法来处理鼠胸腺细胞,结果显示:3处理组的MTT(OD)值(0.335 ± 0.021)高于4处理组(MTT(OD): 0.283 ± 0.031)和2处理组(MTT(OD):0.247 ± 0.025),表明3在促进鼠胸腺细胞活力方面优于2 和 4。 相似文献
979.
We study the L^l-error estimates for the upwind scheme to the linear advection equations with a piecewise constant coefficients modeling linear waves crossing interfaces. Here the interface condition is immersed into the upwind scheme. We prove that, for initial data with a bounded variation, the numerical solution of the immersed interface upwind scheme converges in L^l-norm to the differential equation with the corresponding interface condition. We derive the one-halfth order L^l-error bounds with explicit coefficients following a technique used in [25]. We also use some inequalities on binomial coefficients proved in a consecutive paper [32]. 相似文献
980.
Histone deacetylases (HDACs) play an important role in tumorigenesis. Inhibition of HDACs is considered as a potent strategy for cancer therapy. Two lead compounds (ja and jb) were found to have activities against HDACs with IC50 at about 15 μmol/L. Then a new series of hydroximic acid derivatives were designed and synthesized based on them. The HDACs activity assay in vitro found that compounds J04 and ,109 are nearly as potent as the positive control drug Zolinza. 相似文献