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51.
Yonggang Shangguan Li Zhao Liyang Tao Qiang Zheng 《Journal of Polymer Science.Polymer Physics》2007,45(13):1704-1712
The effects of preparation method, composition, and thermal condition on formation of β‐iPP in isotactic polypropylene/ethylene–propylene rubber (iPP/EPR) blends were studied using modulated differential scanning calorimeter (MDSC), wide angle X‐ray diffraction (WAXD), and phase contrast microscopy (PCM). It was found that the α‐iPP and β‐iPP can simultaneity form in the melt‐blended samples, whereas only α‐iPP exists in the solution‐blended samples. The results show that the formation of β‐iPP in the melt‐blended samples is related to the crystallization temperature and the β‐iPP generally diminishes and finally vanishes when the crystallization temperature moves far from 125 °C. The phenomena that the lower critical temperature of β‐iPP in iPP/EPR obviously increases to 114 °C and the upper critical temperature decreases to 134 °C indicate the narrowing of temperature interval, facilitating the formation of β‐iPP in iPP/EPR. Furthermore, it was found that the amount of β‐iPP in melt‐blended iPP/EPR samples is dependent on the composition and the maximum amount of β‐iPP formed when the composition of iPP/EPR blends is 85:15 in weight. The results through examining the effect of annealing for iPP/EPR samples at melt state indicate that this annealing may eliminate the susceptibility to β‐crystallization of iPP. However, only α‐iPP can be observed in solution‐blended samples subjected to annealing for different time. The PCM images demonstrate that an obvious phase‐separation happens in both melt‐blended and solution‐blended iPP/EPR samples, implying that compared with the disperse degree of EPR in iPP, the preparation method plays a dominant role in formation of β‐iPP. It is suggested that the origin of formation of β‐iPP results from the thermomechanical history of the EPR component in iPP/EPR. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1704–1712, 2007 相似文献
52.
The crystallization behavior of miscible syndiotactic polystyrene (sPS) and atactic polystyrene (aPS) blends with different sPS/aPS weight ratios was investigated in supercritical CO2 by using Fourier‐transform infrared spectroscopy, differential scanning calorimetry, and wide‐angle X‐ray diffraction. Supercritical CO2 and aPS exhibited different effects on the conformational change of sPS and competed with each other. Increasing the content of amorphous aPS in the blends made its effect on the conformational change of sPS gradually surpass that of supercritical CO2. Supercritical CO2 favored the formation of the helical conformation of sPS in lower temperature range and the all trans planar conformation in higher temperature range, instead of forming the latter one only in higher temperature range in ambient atmosphere. However, increasing aPS content in the blends pushed the range for forming the helical conformation to lower temperature and made the all trans planar conformation dominant in aPS/sPS 25/75 blend after treating in supercritical CO2 above 60 °C. The all trans planar zigzag conformation was more favorable than the helical conformation after mixing aPS in sPS in supercritical CO2. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1755–1764, 2007 相似文献
53.
The clusters of Eu3+ ion in Eu(DBM)3Phen-doped polymethyl methacrylate (PMMA) have been studied by three means. The relative fluorescence intensity ratio of the 5D0 → 7F2 to 5D0 → 7F1 transitions with different concentrations of Eu3+ in Eu(DBM)3Phen-doped PMMA and metastable-state (5D0) lifetime dependence on Eu3+ concentration are analyzed. The analysis indicates that there are no clustering effects in Eu3+ ions of Eu(DBM)3Phen-doped PMMA when the Eu3+ doping concentration is up to 1.0 wt.-%. At the same time, the clustering effect has not been observed by the scanning near-field optical microscopy (SNOM) in Eu(DBM)3Phen-doped PMMA with 1.0 wt.-% of Eu3+ ions. The analysis reveals that a high concentration of Eu3+ can be incorporated into polymer optical fiber (POF) without clustering effect.OCIS codes: 180.5810, 300.6280, 250.5460, 160.5690. 相似文献
54.
The central zinc(II) atom in the title complex is tetrahedrally coordinated by four nitrogen atoms derived from 4‐methyl‐5‐imidazolecarboxyaldehyde ligands with Zn? N in the range 2.007(3) to 2.026(4) Å. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
55.
A series of 4,6-disubstituted pyrimidines were synthesized via Suzuki and Kumada coupling reaction of 4,6-dichloropyrimidine. 相似文献
56.
Zheng Yu 《manuscripta mathematica》2003,111(2):163-186
In this paper, the negative gradient flow for the L
2-integral of Ricci curvature on a 3-manifold is considered. It is not known whether the solution to this fourth order geometric
evolution equation exists, and whether it will develop singularities in finite time. Based on the trick of De Turck and the
idea of Hamilton on the flow of Ricci curvature, the local existence on any compact Riemannian manifold is obtained. In addition,
the conditions for the occurences of singularities in finite time during the evolution and the asymptotic behavior of the
flow on a 3-manifold are discussed.
Received: 22 April 2002 / Revised version: 5 January 2003
Published online: 24 April 2003
This work is partially supported by the Foundations of NNSF of China, the Foundation for University Key Teacher by MEC and
Shanghai Priority Academic Discipline. 相似文献
57.
本在Glover—Klingman算法及最小费用支撑树对策的基础上,讨论了最小费用k度限制树对策问题.利用威胁、旁支付理论制订了两种规则,并利用优超、策略等价理论分别给出了在这两种规则下最小费用k度限制树对策核心中的解,从而证明了在这两种规则下其核心非空. 相似文献
58.
59.
Jia‐Yuh Sheu Yeh‐Long Chen Cherng‐Chyi Tzeng Shu‐Lin Hsu Kuo‐Chang Fang Tai‐Chi Wang 《Helvetica chimica acta》2003,86(7):2481-2489
Certain 1‐ethyl‐ and 1‐aryl‐6‐fluoro‐1,4‐dihydroquinol‐4‐one derivatives were synthesized and evaluated for antimycobacterial and cytotoxic activities. Preliminary results indicated that, for 1‐aryl‐6‐fluoroquinolones, both 7‐(piperazin‐1‐yl)‐ and 7‐(4‐methylpiperazin‐1‐yl) derivatives, 9b and 11a , are able to completely inhibit the growth of M. tuberculosis at a concentration of 6.25 μg/ml, while the 7‐[4‐(2‐oxo‐2‐phenylethyl)piperazin‐1‐yl] derivative 13 exhibits only 31% growth inhibition at the same concentration. For 1‐ethyl‐6‐fluoroquinolones, both 7‐[4‐(2‐oxopropyl)piperazin‐1‐yl]‐ and 7‐[4‐(2‐oxo‐2‐phenylethyl)piperazin‐1‐yl]‐derivatives, 2a and 2b , respectively, show complete inhibition, while their 2‐iminoethyl and substituted phenyl counterparts 3a and 2c are less active. In addition, the 6,8‐difluoro derivative was a more‐favorable inhibitor than its 6‐fluoro counterpart ( 2b vs. 2d ). These results deserve full attention especially because 2a, 2b, 9b , and 11a are non‐cytotoxic at a concentration of 100 μM . Furthermore, compound 9b proved to be a potent anti‐TB agent with selective index (SI)>40 and an EC90 value of 5.75 μg/ml. 相似文献
60.
The dominant decay modes of charged top-pions (π±t ) are tb or ~b. We consider the single production ofcharged top-pions in association with a top quark via e+ e- annihilation and calculate the production cross section of theprocesses e+ e- → t-bπ+ (tb-π-) at the leading order. We find that it can reach 1.2 fb with reasonable parameter values.The charged top-pions may be detected via the channel tbπ± in the future high energy e+ e- colliders. 相似文献