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101.
Yusa H Shirako Y Akaogi M Kojitani H Hirao N Ohishi Y Kikegawa T 《Inorganic chemistry》2012,51(12):6559-6566
High-pressure structural phase transitions in NaNiF(3) and NaCoF(3) were investigated by conducting in situ synchrotron powder X-ray diffraction experiments using a diamond anvil cell. The perovskite phases (GdFeO(3) type) started to transform into postperovskite phases (CaIrO(3) type) at about 11-14 GPa, even at room temperature. The transition pressure is much lower than those of oxide perovskites. The anisotropic compression behavior led to heavily tilted octahedra that triggered the transition. Unlike oxide postperovskites, fluoropostperovskites remained after decompression to 1 atm. The postperovskite phase in NaCoF(3) broke down into a mixture of unknown phases after laser heating above 26 GPa, and the phases changed into amorphous ones when the pressure was released. High-pressure and high-temperature experiments using a multianvil apparatus were also conducted to elucidate the phase relations in NaCoF(3). Elemental analysis of the recovered amorphous samples indicated that the NaCoF(3) postperovskite disproportionated into two phases. This kind of disproportionation was not evident in NaNiF(3) even after laser heating at 54 GPa. In contrast to the single postpostperovskite phase reported in NaMgF(3), such a postpostperovskite phase was not found in the present compounds. 相似文献
102.
Takumi Watanabe Yuji Tsunoda Akira Matsuo Kenji Sugiyama Akira Hirao 《Macromolecular Symposia》2006,240(1):23-30
A series of dendrimer-like star-branched poly(methyl methacrylate)s (PMMA)s of generations consisting of four branched segments at each junction have been successfully synthesized by developing an iterative methodology. It involves two reaction steps in each iterative reaction sequence, (a) a coupling reaction of the α-functionalized living anionic PMMA with four tert-butyldimethylsilyloxymethylphenyl (SMP) groups with benzy bromide (BnBr)-chain-functionalized PMMA and (b) a transformation of SMP group into BnBr functionality. By repeating the reaction sequence thrice, the above-mentioned dendrimer-like star-branched (PMMA)s of up to third-generation made up of 4, 20, and 84 PMMA segments and 16, 64, and 256 BnBr termini were synthesized by the first, second, and third iterative processes, respectively. The resulting polymers all were well-defined in branched architecture and precisely controlled in chain length. 相似文献
103.
In order to achieve the successive synthesis of star-branched polymers, we have developed a new iterative methodology which involves only three sets of the reactions in each iterative process: (a) a coupling reaction of a living anionic polymer with 1,1-bis(3-chloromethylphenyl)ethylene to prepare a DPE-chain-functionalized polymer, (b) an addition reaction of sec-BuLi to the DPE-chain-functionalized polymer, followed by treatment with 1-(4-(4-bromobutyl)phenyl)-1-phenylethylene to prepare a new DPE-chain-functionalized polymer whose DPE is separated by four methylene units from the main chain, and (c) a coupling reaction of 1,1-bis(3-chloromethylphenyl)ethylene with the polymer anion derived from the newly prepared DPE-chain-functionalized polymer and sec-BuLi. With this methodology, a series of well-defined 4-arm, 8-arm, and 16-arm regular star-branched polystyrenes as well as 4-arm A2B2, 8-arm A4B4, and 16-arm A8B8 asymmetric star-branched polymers comprising polystyrene and poly(α-methylstyrene) segments have been successively synthesized. 相似文献
104.
Tomoya Higashihara Akira Hirao 《Journal of polymer science. Part A, Polymer chemistry》2004,42(18):4535-4547
A series of four-armed A2BC, AB2C, and ABC2 asymmetric star-branched polymers with a three-component system, the A, B, and C segments of which are polystyrene, polyisoprene, and poly(4-trimethylsilylstyrene), respectively, have been successfully synthesized with a methodology based on living anionic polymerization with dual-functionalized 1,1-bis(3-chloromethylphenyl)ethylene ( 1 ). These star-branched polymers have well-defined architectures and precisely controlled chain lengths, as confirmed by size exclusion chromatography, 1H and 13C NMR, vapor pressure osmometry, and static light scattering analyses. A simple and convenient one-pot process for star-branched polymer synthesis is an additional advantage of this methodology. One problem to be solved is that the synthetic route is limited in some cases by the inherently low reactivity of polyisoprenyllithium toward the 1,1-diphenylethylene functionality of in-chain-functionalized polymers. A new four-armed ABCD star-branched polymer, the A, B, C, and D segments of which are polyisoprene, poly(4-methoxystyrene), polystyrene, and poly(4-trimethylsilylstyrene), could also be synthesized through the extension of the methodology using 1 to a four-component system. The successful results strongly demonstrate the synthetic versatility and potential of this methodology for a wide variety of well-defined asymmetric star-branched polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4535–4547, 2004 相似文献
105.
106.
Several substituted oxetanes were treated with lithium acetylides in the presence of boron trifluoride etherate to give f-hydroxyacetylenes. The reaction conditions were varied and several synthetic features of the present reaction were revealed. 相似文献
107.
The long-range correction (LC) scheme of density-functional theory (DFT) was applied to the calculation of the pi-aromatic interaction of the benzene dimer and naphthalene dimer. In previous calculations, it was confirmed that the LC scheme [Iikura et al., J. Chem. Phys. 115, 3540 (2001)] gives very accurate potential- energy surfaces (PESs) of small van der Waals (vdW) complexes by combining with the Anderson-Langreth-Lundqvist (ALL) vdW correlation functional [Andersson et al., Phys. Rev. Lett. 76, 102 (1996)] (LC-DFT + ALL). In this study, LC-DFT+ALL method was examined by calculating a wide range of PES of the benzene dimer including parallel, T-shaped, and parallel-displaced configurations. As a result, we succeeded in reproducing very accurate PES within the energy deviance of less than 1 kcalmol in comparison with the results of high-level ab initio molecular-orbital methods at all reference points on the PES. It was also found that LC-DFT + ALL gave accurate results independent of exchange-correlation functional used, in contrast with the strong functional dependencies of conventional pure functionals. This indicates that both exchange repulsion and van der Waals attractive interactions should be correctly incorporated in conventional pure functionals in order to calculate accurate pi-aromatic interactions. We also found that LC-DFT + ALL method has a low basis-set dependency in the calculations of pi-aromatic interactions. The present scheme was also successfully applied to the pi,[ellipsis (horizontal)],pi stacking interactions of naphthalene dimer. This may suggest that LC-DFT + ALL method would be a powerful tool in the calculations of large molecules such as biomolecules. 相似文献
108.
109.
Kazuyoshi?KanamoriEmail author Kazuki?Nakanishi Kazuyuki?Hirao Hiroshi?Jinnai 《Journal of Sol-Gel Science and Technology》2005,35(3):183-191
A sharp transition to pillar structure has been observed in simple sol-gel systems accompanying phase separation inside rectangular-sectioned open grooves which were fabricated on a silica glass chip. The structural variation was investigated using two contrastive systems; one with a rapid sol-gel reaction and the other with a sluggish reaction. In the slower system, transition from web-like bicontinuous structure to pillar structure, we call it as “web-to-pillar transition”, occurred when the bulk characteristic length Λm exceeded the width of the groove D. On the other hand, the transition did not occur in the same condition in the faster system; it occurred when Λm became much longer than D. A consistent formation mechanism model was also proposed using a relation between interfacial curvatures and pressure. 相似文献
110.
The U+O chemi-ionization reaction has been investigated by quantum chemical methods. Potential-energy curves have been calculated for several electronic states of UO and UO(+). Comparison with the available spectroscopic and thermodynamic values for these species is reported and a mechanism for the chemi-ionization reaction U+O-->UO(+)+e(-) is proposed. The U+O and Sm+O chemi-ionization reactions are the first two metal-plus-oxidant chemi-ionization reactions to be studied theoretically in this way. 相似文献