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61.
Sheng‐Huei Hsiao Chien‐Wei Chen Guey‐Sheng Liou 《Journal of polymer science. Part A, Polymer chemistry》2004,42(13):3302-3313
Two new diamines, 2,4‐diaminotriphenylamine ( 3 ) and N‐(2,4‐diaminophenyl)carbazole ( 4 ), were synthesized via the cesium fluoride‐mediated aromatic substitution reactions of 1‐fluoro‐2,4‐dinitrobenzene with diphenylamine and carbazole, followed by palladium‐catalyzed hydrazine reduction. Amorphous and soluble aramids having pendent diphenylamino and carbazolyl groups were prepared by the phosphorylation polycondensation of aromatic dicarboxylic acids with diamines 3 and 4 , respectively. The aramids derived from diamine 3 had sufficiently high molecular weights to permit the casting of flexible and tough films. They exhibited excellent mechanical properties and moderately high softening temperatures in the 221–298 °C range. However, the reactions of diamine 4 with aromatic diacids gave relatively lower molecular weights products that could not afford flexible films. For a comparative purpose, the parent aramids derived from m‐phenylenediamine and aromatic diacids were also prepared and characterized. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3302–3313, 2004 相似文献
62.
In this research, a simple, sensitive chemiluminescence (CL) method for the determination of humic acid (HA) in water samples was first developed based on the redox reaction between humic acid and cerium(IV) in the acidic condition. Different with the former redox CL reaction which occurred in alkaline solution, no enhancers were needed and neither precipitation nor a second contamination would occur in the present CL system. Comparing with other spectrometric methods, we find that the proposed analysis system had better applicability and accuracy. Under the optimal experiment conditions, the CL peak height was linear with the concentration of HA in the range of 0.03 to 10.0 microg mL(-1). The detection limit is 0.01 microg mL(-1) (S/N = 3), and the relative standard deviation was 2.3% for 0.5 microg mL(-1) HA solution with eleven repeated measurements. The present CL method was successfully applied to the determination of HA in tap water, spring water and river water samples with good recovery from 90.0 to 110.0%. A possible CL mechanism was proposed based on the results of UV and fluorescence spectrometry and the CL spectrum of HA. It was speculated that the semi-quinone radicals in the excited state were the emitters. 相似文献
63.
本文采用解析的方法计算了应变Si1-xGex层中p型杂质电离度与Ge组分x、温度T以及掺杂浓度N的关系.发现常温时,在同一Ge组分下,随着掺杂浓度的升高,杂质的电离度的先变小,而后又迅速上升到1.在同一掺杂浓度下,轻掺杂时,杂质的电离度随Ge组分的增加先变大,而后几乎不变;重掺杂时,杂质电离能变为0后,杂质电离度为1.低温下,轻掺杂时,载流子低温冻析效应较为明显,杂质的电离度普遍较小,当掺杂浓度大于Mott转换点时,载流子冻析效应不再明显,电离率迅速上升到1.在同一Ge组分下,随着掺杂浓度的升高,杂质的电离度先变小,后变大,而后又迅速上升到1.在同一掺杂浓度下,轻掺杂时,杂质的电离度随Ge组分的增加变大;重掺杂时,杂质电离能变为0后,杂质电离度为1. 相似文献
64.
Xiao‐Hui Liu Yan‐Guo Li Ying Lin Yue‐Sheng Li 《Journal of polymer science. Part A, Polymer chemistry》2007,45(7):1272-1281
The reversible addition–fragmentation chain transfer (RAFT) polymerization of acrylonitrile (AN) mediated by 2‐cyanoprop‐2‐yl dithiobenzoate was first applied to synthesize polyacrylonitrile (PAN) with a high molecular weight up to 32,800 and a polydispersity index as low as 1.29. The key to success was ascribed to the optimization of the experimental conditions to increase the fragmentation reaction efficiency of the intermediate radical. In accordance with the atom transfer radical polymerization of AN, ethylene carbonate was also a better solvent candidate for providing higher controlled/living RAFT polymerization behaviors than dimethylformamide and dimethyl sulfoxide. The various experimental parameters, including the temperature, the molar ratio of dithiobenzoate to the initiator, the molar ratio of the monomer to dithiobenzoate, the monomer concentration, and the addition of the comonomer, were varied to improve the control of the molecular weight and polydispersity index. The molecular weights of PANs were validated by gel permeation chromatography along with a universal calibration procedure and intrinsic viscosity measurements. 1H NMR analysis confirmed the high chain‐end functionality of the resultant polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1272–1281, 2007 相似文献
65.
Chang-jian Zhao 《中国科学A辑(英文版)》2007,50(9):1347-1360
In this paper, we first introduce a concept of L
p
-dual Quermassintegral sum function of convex bodies and establish the polar projection Minkowski inequality and the polar
projection Aleksandrov-Fenchel inequality for L
p
-dual Quermassintegral sums. Moreover, by using Lutwak’s width-integral of index i, we establish the L
p
-Brunn-Minkowski inequality for the polar mixed projection bodies. As applications, we prove some interrelated results.
This work was partially supported by the National Natural Science Foundation of China (Grant No. 10271071), Zhejiang Provincial
Natural Science Foundation of China (Grant No. Y605065) and Foundation of the Education Department of Zhejiang Province of
China (Grant No. 20050392) 相似文献
66.
The spin coating method was used to assemble polymer (Poly (2,5-dibutoxy-1,4-phenylenevinylene)) (DBO-PPV) into the pores of porous alumina which was prepared by anodization. Four peaks in the photoluminescence (PL) spectra of the composite, with contributions from the DBO-PPV and porous alumina, were found. It was also found that the light emitting from the porous alumina could excite the photoluminescence of DBO-PPV. The nanometer effect of the porous alumina can lead to a blue shift of 90 nm of the PL peaks of DBO-PPV. 相似文献
67.
Natural convections in conjugated single and double enclosures 总被引:7,自引:0,他引:7
The natural convection in single and double conjugated enclosures are numerically investigated. The single and double enclosures are formed by low conductance walls with finite thickness. The outside vertical surfaces of the conducting walls are of the third kind of boundary condition while the top and bottom outside surfaces are adiabatic. The problem studied is characterized by a dominant horizontal temperature gradient and the thermal boundary conditions at the cavity surfaces can not be specified in priori. Numerical results reveal the characteristics in such kind of enclosures and show the importance of the thermal boundary conditions on the natural convection in enclosures. It is also found that the natural convections in the conjugated double enclosures are basically the same, with a major difference in their fluid temperature levels. 相似文献
68.
69.
Liang Zhao 《Tetrahedron letters》2006,47(19):3291-3294
Allylmagnesium, allylindium, and allylbismuth generally showed a preference for axial addition to cyclohexenones. Allylmagnesium was the most stereoselective. Reactions with an α-methylated enone (carvone) were the most selective, except that allylbismuth was unreactive with this substrate. 相似文献
70.
ZnO naorods on ZnO-coated seed substrates were fabricated by solution chemical method from Zn(NO3)2/NaOH under assisted electrical field. The working mechanism of electrical field was analyzed and the factors affecting the rod growth such as potential, precursor concentration and growth temperature were elucidated. The structural and optical properties are characterized by SEM, TEM, XRD, HRTEM and UV-vis. The results indicated that the nanorods have wurtzite structure without electrical field and are primarily of zincite structure under electrical field; when the electrical field is 1.1-1.3 V, not only the elevation of ion diffusion and adsorption lower the crystallite/solution interfacial energy and then the crystal nucleation barrier by increasing charge intensity, but also the production of H+ through oxidation of OH− increases properly the degree of solution supersaturation near the substrate, and thus lowers the activation energy. Both the two processes do favor to rod growth. With increasing precursor concentration in this system, the average diameter and length of ZnO nanorods increase, leading to decreasing of optical transmittance. The maximum rod growth rate at given concentration of Zn2+ occurs at a specific temperature. 相似文献