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971.
Guillaume Desurmont Motomi Tanaka Yong Li Hajime Yasuda Tohru Tokimitsu Seiji Tone Akira Yanagase 《Journal of polymer science. Part A, Polymer chemistry》2000,38(22):4095-4109
This paper describes the first examples of ABA‐ and AB‐type block copolymerizations of a nonpolar monomer, in this case ethylene, with polar monomers, such as methyl methacrylate (MMA), ϵ‐caprolactone (CL), and 2,2‐dimethyltrimethylene carbonate (DTC), initiated by the unique catalytic function of rare earth metal complexes [Sm(II) and Ln(III) (Ln = Y, Sm)] as initiators. The Sm(II) species conducts the ABA‐type triblock copolymerization, leading to poly(MMA‐co‐ethylene‐co‐MMA), poly(CL‐co‐ethylene‐co‐CL), or poly(DTC‐co‐ethylene‐co‐DTC) by the efficient catalysis of racemic Me2Si(C5H2‐2‐Me3Si‐4‐tBu)2Sm(THF)2 ( 1 ) or meso Me2Si(Me2SiOSiMe2)(C5H2‐3‐tBu)Sm(THF) ( 2b ). The resulting block copolymers are completely insoluble in THF and CHCl3, but the homopolymers of MMA, CL, and DTC are freely soluble in these solvents. TEM profiles provide direct evidence for the block copolymerizations, where the spheric morphology of homogeneously dispersed polar polymers was observed. Ln(III) species, such as racemic Me2Si(C5H2‐2‐Me3Si‐4‐tBuMe2Si)YH ( 5 ) and Me2Si(C5H2‐2‐Me3Si‐4‐tBu)SmH ( 6 ), afford AB‐type block copolymers between ethylene and MMA or CL, whose TEM images reveal the homogeneous dispersion of poly(MMA) or poly(CL) units in the polyethylene region. The ABA‐ and AB‐type block copolymers demonstrate high break stress and high tensile modulus as compared with their corresponding blended polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4095–4109, 2000 相似文献
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974.
E. J. Corey Weidong Li Tohru Nagamitsu 《Angewandte Chemie (International ed. in English)》1998,37(12):1676-1679
A selective, irreversible inhibitor of proteasome function , lactacystin ( 1 ) is an important experimental tool in cell biology. An efficient and direct enantioselective synthesis of lactacystin proceeds via the intermediates shown below. This process allows for the first time easy access to analogues of lactacystin in which the isopropyl substituent is replaced by other lipophilic groups. PMB=p-methoxybenzyl. 相似文献
975.
976.
Hiroki Murase Takuji Kume Takeji Hashimoto Yasuo Ohta Tohru Mizukami 《Macromolecular Symposia》1996,104(1):159-182
The shear-induced concentration fluctuations or phase separation of a semidilute solution comprised of polystyrene (PS) as a solute and dioctylphthalate (DOP) as a solvent (PS/DOP) was investigated by using real-time and in-situ shear-small-angle light scattering and shear-phase-contrast optical microscopy. When a transient shear flow with a fixed shear rate γ greater than a critical value γC was imposed on the solution, a unique anisotropic scattering pattern was observed some time after onset of shear. This pattern was found to be identical to the “butterfly pattern” previously reported for the same solutions under steady shear flow with γC. When the shear flow was ceased before the scattered intensity reached a steady state, the scattered intensity rapidly increased toward a maximum intensity, and then decreased toward the intensity of the quiescent solution with time. From the phase-contrast microscopy, this immediate increment of the scattered intensity after the shear cessation was found to arise from the increment in amplitude of the concentration fluctuations along flow direction. The characteristic length scale of the fluctuations was about 2.5 μm in this experiment, almost independent of the shear rate imposed on the solution. 相似文献
977.
Michiya Hayakawa Makoto Mitani Tohru Yamada Teruaki Mukaiyama 《Macromolecular rapid communications》1996,17(12):865-870
Living ring-opening polymerization of the cyclic carbonate 1,3-dioxepan-2-one was achieved by using the cationic zirconocene complex [Cp2ZrMe]+[B(C6F5)4]− as catalyst at room temperature. A linear relation between conversion and molecular weight of the obtained polymer was observed. Furthermore, block copolymerization of the cyclic carbonate and ε-caprolactone was successfully performed. 相似文献
978.
Osamu Ishikawa Hitoshi Inaba Kenji Kawasaki Shouichi Miyawaki Akira Matsubara Tohru Hata Takao Kodama 《Physica B: Condensed Matter》2000,280(1-4):89-90
We have measured spin diffusion coefficients of liquid 3He at a frequency of 920 kHz by pulsed NMR. By analyzing our data in the framework of the Leggett–Rice theory we got a spin diffusion coefficient and a Leggett–Rice parameter =λωτ simultaneously at each temperature. On approaching the superfluid transition the spin diffusion coefficients showed a deviation from predictions of the Fermi liquid theory. The deviation at low pressure was larger than that at high pressure. This anomaly may be due to the effects of fluctuations of superfluidity which were recently observed in the viscosity measurement of liquid 3He. 相似文献
979.
We study flat directions and soft scalar masses using a Z3 orbifold model with SU(3) × SU(2) × U(1) gauge group and extra gauge symmetries including an anomalous U(1) symmetry. Soft scalar masses contain D-term contributions and particle mixing effects after symmetry breaking and they are parametrized by a few parameters. Some specific relations among scalar masses are obtained. 相似文献
980.