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991.
992.
Possible coadsorption states of Ti mononuclear species and ethyl benzoate (EB) and their interaction on MgCl2 (110) and (100) surfaces were investigated with periodic density functional calculations in order to obtain the microscopic understanding about how EB affects the steric and electronic natures of the Ti species. EB was unlikely to be attached to the TiCl4 species on both the MgCl2 (110) and (100) surfaces. The coadsorption of EB at Mg2+ ions near the Ti species was as favorable as the separate adsorption, which implied the random placement of these adsorbants in the final catalyst. The charge redistributions upon coadsorption among the Ti species, EB and the support were found to be dependent on the surface structures: the electron density of the Ti speceies was rather decreased by the coadsorption on the (100) surface, while that of the Ti species was enhanced due to the support-mediated electron transfer from EB on the (110) surface. It was suggested that the presence of EB close to the Ti species should generate donor-related active sites selectively on the (110) surface. 相似文献
993.
Satoru Amou Osamu Haba Kaori Shirato Teruaki Hayakawa Mitsuru Ueda Kazuhiko Takeuchi Michihiko Asai 《Journal of polymer science. Part A, Polymer chemistry》1999,37(13):1943-1948
We investigated a head-to-tail regioregularity of poly(3-alkylthiophenes) from 3-alkylthiophene by an oxidative coupling polymerization, which is the simplest and easiest way for the synthesis of polythiophenes. The polymerizations were conducted using ferric chloride (III) as an oxidant in chloroform. Investigating the polymerization conditions, a lower temperature and a lower concentration were effective for increasing the head-to-tail (HT) content. The best HT content of 88% was obtained when the temperature was −45°C and the initial monomer concentration was 0.02 mol L−1. Washing the resulting polymer by n-hexane further increased the content to 91%. Thus, it was found that the high regioselectivity can be achieved by the simple polymerization and the simple operation such as washing. The polymerization mechanism causing the regularity is also discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1943–1948, 1999 相似文献
994.
Tamotsu Hashimoto Toshiaki Iwata Noriyuki Uchiyama Toshiyuki Kodaira 《Journal of polymer science. Part A, Polymer chemistry》1999,37(15):2923-2932
Effects of steric crowding of the substituent of carboxylate counteranions on living cationic polymerization of isobutyl vinyl ether (IBVE) were investigated with the use of two series of carboxylic acids with various carbonyl substituents [RCOOH; R = (aliphatic series) CH3CH2, (CH3)2CH, (CH3)3C; (aromatic series) C6H5CH2, (C6H5)2CH, (C6H5)3C] in conjunction with tin tetrabromide (SnBr4) and 1,4-dioxane (DO) in toluene at 0°C. The overall polymerization rate increased with increasing the bulkiness of the substituents R in both the series: R = CH3 (1) ≃ CH3CH2 (1) < (CH3)2CH (1.76) < (CH3)3C (2.31); C6H5CH2 (0.84) < (C6H5)2CH (0.98) < (C6H5)3C (1.74); the values in the parentheses show the relative polymerization rate. In all the polymerizations, the number-average molecular weight (Mn) of the polymers was directly proportional to monomer conversion and in good agreement with the calculated values, assuming that one RCOOH molecule forms one polymer chain. The living nature of these polymerizations was further confirmed by a linear increase in Mn of the polymers upon sequential addition of a fresh monomer feed to the almost completely polymerized reaction mixtures. In the polymerizations with sterically less hindered carboxylic acids [R = CH3CH2, (CH3)2CH, C6H5CH2, (C6H5)2CH], the molecular weight distribution (MWD) of the polymers was very narrow (Mw/Mn < 1.1) throughout the polymerizations. In contrast, with bulkier substituent-containing counterparts [R = (CH3)3C, (C6H5)3C], the polymerizations led to the polymers of relatively broad MWD (Mw/Mn ≅ 1.5 at ca. 100% monomer conversion). The bulky substituents such as (CH3)3C and (C6H5)3C may decrease the interconversion rate between a dormant and an active species and increase the time-average concentration of the active growing species. The stereoregularity of the obtained polymers was not changed much with the steric environment of the counteranion (meso: 66–69%). © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2923–2932, 1999 相似文献
995.
A stereoregular and Bernoullian copolymer of styrene and ethylene was produced by the catalyst system of rac-[isopropylidenebis(1-indenyl)]zirconium dichloride and MAO. This catalyst system yields a high molecular weight copolymer with good activity at 50°C. The copolymer consists of Et-Et, St-Et, and head to tail St-St sequences and has a highly isotactic Et-St alternating sequence. This copolymer shows a melting point (80 – 110°C), due to the isotactic alternating sequence. 相似文献
996.
Toshiaki Mori Yusuke Yoshigoe Yoichiro Kuninobu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(41):14599-14603
Multicolor emissive materials consisting of a single luminophore, a Lewis acid, and their complex were developed. The emission colors can be tuned by changing the concentration of the solution and the ratio of mixed solvents. Various emission colors in the solid state were observed when the complexes were added to polymers in different amounts. The color change is due to equilibrium disruption between the single luminophore, the Lewis acid, and the complex thereof. White emission was observed by appropriately controlling the equilibrium by changing the amount of the complex in the polymer. 相似文献
997.
T. Sekine S. Ichikawa A. Osa M. Koizumi H. Iimura K. Tsukada I. Nishinaka Y. Hatsukawa Y. Nagame M. Asai Y. Kojima T. Hirose M. Shibata H. Yamamoto K. Kawade 《Journal of Radioanalytical and Nuclear Chemistry》1999,239(1):127-131
Studies on the decay of unstable nuclei using the two on-line isotope separators of JAERI are reviewed for the past five years. With the previously established ion-source technique using mono-oxide ion formation in a thermal ion source, the new nuclides125Pr and127Pr have been identified in heavy-ion fusion residues. Further, with a newly developed gas-jet coupled thermal ion source, the new nuclides166Tb,165Gd,161Sm and236Am have been identified by bombarding238U and235U targets with a proton or6Li beam. Other studies, including off-line experiments, by decay spectroscopy, laser spectroscopy and Mössbauer spectroscopy are described. 相似文献
998.
Toshiaki Kakitani Yoshitaka Beppu Atsushi Yamada 《Photochemistry and photobiology》1999,70(4):686-693
We investigated the molecular mechanism of a rather large red shift of 31 nm in a human red pigment compared with a human green pigment. In this analysis, we paid special attention to the phenomenon of nonadditivity of spectral shifts due to substitution of the key amino acids (OH-bearing amino acids) and the phenomenon of cooperativity by which the spectral shifts due to substitution of the key amino acids in the protein environment of red pigment are about 1.5 times larger than that in the protein environment of green pigment. The analysis was made by using a model of three active sites on which the key amino acids are located and four effective sites by which the effect of the key amino acids is modified. As a result, we found that the interaction between the active sites that occurs through the repolarization of the chromophore induced by the key amino acid is essential for the nonadditivity phenomenon. We also found that the interaction between the active site and the effective site plays a major role in the cooperativity phenomenon. More directly, we say that the highly polarizable property of the chromophore is the origin of the rather large red shift in red pigment. Based on these analyses, we conclude that the interaction between the polarizable chromophore and the protein moiety has the capability of producing a significant spectral shift, at least 1000 cm-1, even by substitution of moderate polar residues of the OH-bearing amino acids. 相似文献
999.
A comparison is made between two types of solid particles used in electrorheological fluids: particles with homogeneous electrical
properties versus layered particles with a semi-conducting core surrounded by an outer layer of lower conductivity. Rheological
measurements of these suspensions under steady shear and d.c. electric field show that the layered particle system produces
the same yield stress but with a substantially reduced electric current. X-ray spectroscopic analysis confirms that these
particles have a thin layer of SiOx on the outer surface which causes the reduction in conductivity. Measurement of the dielectric permittivity followed by analysis
using the Maxwell-Wagner model of polarization indicates that the conductivity of the outer layer is about 0.62 times that
of the core region.
Received: 13 January 1999 Accepted: 26 July 1999 相似文献
1000.
The formation of colloidal silver in the presence of a nonionic surfactant, Surfynol 465, was studied at various temperatures. By simply mixing equal volumes of AgClO4 aq. (1–10 mmol kg–1) and Surfynol 465 aq., the colloidal silver was formed. The colloidal solution had well over ten times the amount of fine silver particles in the solution formed by the ordinary methods. The first factor to form the colloidal silver without aggregation was the molar ratio of Surfynol 465 to AgClO4, and the optimum ratio increased with increasing the concentration of AgClO4 or the temperature. In the fraction of colloidal silver collected through the gel filtration, Surfynol 465 was also found in the micellar state. From these results, it was suggested that Surfynol 465 was a protecting agent of colloidal silver as well as a reducing agent of AgClO4 in the similar manner to the case of colloidal gold. 相似文献