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排序方式: 共有314条查询结果,搜索用时 15 毫秒
71.
Mitsuo Sawamoto Etsu Takeuchi Tamotsu Hashimoto Toshinobu Higashimura 《Journal of polymer science. Part A, Polymer chemistry》1987,25(10):2717-2727
Cationic polymerization of 2-vinyloxyethyl glycidyl ether (VEGE), a vinyl ether with an epoxy group, was conducted with various initiators in CH2Cl2 in the temperature range from +15 to ?78°C, and the possibility of its selective vinyl polymerization was investigated. BF3OEt2 polymerized both vinyl and epoxy groups of VEGE to yield polymers partially insoluble in organic solvents. HI/I2, iodine, and CF3SO3H gave soluble, low-molecular-weight oligomers with epoxy pendants. 1H-NMR structural analysis of the oligomeric products showed that the epoxy/vinyl ratio of the pendants decreases in the order: 100% epoxy ~ CF3SO3H > HI/I2 ~ I2 ? BF3OEt2. Although HI/I2 or iodine mainly polymerized the vinyl group, the reaction of the vinyl ether-type growing end with an epoxy group of VEGE took place during the polymerization, so that the monomer conversion leveled off at about 40%. 相似文献
72.
We have investigated the influences of the magnetic field strength, shear rate, and random forces on transport coefficients such as viscosity and diffusion coefficient, and also on the orientational distributions of rodlike particles of a dilute colloidal dispersion. This dispersion is composed of ferromagnetic spheroidal particles with a magnetic moment normal to the particle axis. In the present analysis, these spheroidal particles are assumed to conduct the rotational Brownian motion in a simple shear flow as well as an external magnetic field. The basic equation of the orientational distribution function has been derived from the balance of the torques and solved numerically. The results obtained here are summarized as follows. For a very strong magnetic field, the rodlike particle is significantly restricted in the field direction, so that the particle points to a direction normal to the flow direction (and also to the magnetic field direction). However, the present particle does not exhibit a strong directional characteristic, which is one of the typical properties for the previous particle with a magnetic moment parallel to the particle axis. That is, the particle can rotate around the axis of the magnetic moment, although the magnetic moment nearly points to the field direction. The viscosity significantly increases with the field strength, as in the previous particle model. The particle of a larger aspect ratio leads to the larger increase in the viscosity, since such elongated particles induce larger resistance in a flow field. The diffusion coefficient under circumstances of an applied magnetic field is in reasonable agreement between theoretical and experimental results. 相似文献
73.
Toshio Sato Tatsuo Kawara Akira Nishizawa Tamotsu Fujisawa 《Tetrahedron letters》1980,21(35):3377-3380
Optically active terpene such as (R)-(+)-citronellol, (R)-(+)-pulegone or (S)-ar-turmerone is prepared in high enantiomeric excess from an intermediate, (R)-(+)-citronellic acid or (S)-(+)-3-p-tolylbutyric acid, which is easily prepared by the Sn2 type of ring opening reaction of (R)-(+)-β-methyl-β-propiolactone with homoprenylmagnesium bromide in the presence of a copper(I) salt or di-p-tolylcuprate. 相似文献
74.
Tamotsu Hashimoto Toshiaki Iwata Atsushi Minami Toshiyuki Kodaira 《Journal of polymer science. Part A, Polymer chemistry》1998,36(17):3173-3185
Cationic polymerization of isobutyl vinyl ether (IBVE) with acetic acid (CH3COOH)/tin tetrahalide (SnX4: X = Cl, Br, I) initiating systems in toluene solvent at 0°C was investigated, and the reaction conditions for living polymerization of IBVE with the new initiating systems were established. Among these tin tetrahalides, SnBr4 was found to be the most suitable Lewis acid to obtain living poly(IBVE) with a narrow molecular weight distribution (MWD). The polymerization with the CH3COOH/SnBr4 system, however, was accompanied with the formation of a small amount of another polymer fraction of very broad MWD, probably due to the occurrence of an uncontrolled initiation by SnBr4 coupled with protonic impurity. Addition of 1,4-dioxane (1–1.25 vol %) or 2,6-di-tert-butylpyridine (0.1–0.6mM) to the polymerization mixture completely eliminated the uncontrolled polymer to give only the living polymer with very narrow MWD (M w/M n ≤ 1.1; M w, weight-average molecular weight; M n, number-average molecular weight). The M n of the polymers increased in direct proportion to monomer conversion, continued to increase upon sequential addition of a fresh monomer feed, and was in good agreement with the calculated values assuming that one CH3COOH molecule formed one polymer chain. Along with these results, kinetic study and direct 1H-NMR observation of the living polymerization indicated that CH3COOH and SnBr4 act as so-called “initiator” and “activator”, respectively, and the living polymerization proceeds via an activation of the acetate dormant species. The basic additives such as 1,4-dioxane and 2,6-di-tert-butylpyridine would serve mainly as a “suppressor” of the uncontrolled initiation by SnBr4. The polymers produced after quenching the living polymerization with methanol possessed the acetate dormant terminal and they induced living polymerization of IBVE in conjunction with SnBr4 in the presence of 1,4-dioxane. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3173–3185, 1998 相似文献
75.
The dynamic performance (i.e. displacement, current, velocity, and force) of ion‐exchange polymer based actuators (the Nafion?/platinum electrodes) have been examined by developing instrumentation. The CCD imaging technique was examined to evaluate the displacement under the various d.c. potential patterns. Two different d.c. potential patterns with or without a rest were applied to the electrodes at 0.1 Hz. It was better to take a rest at 0 V for the polarization back and forth between +2 and ?2 V to give lower current consumption and longer displacement. The actuator produced the force of ca. 0.95 g at 3.25 V in air. The result also demonstrated that higher overpotential has to be avoided to maintain the maximum force. The generative force is in inverse proportion to the length of the actuators. The dimension of the film strongly governs the force production and its performance. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
76.
Katsuya Ikegami Masato Morifuji Hideki Momose Masahiko Kondow 《Physica E: Low-dimensional Systems and Nanostructures》2006,33(2):381-387
In order to investigate formation process of electronic quantum states in a confined system, we simulate motion of a wavepacket state and show how an eigenstate is formed due to coherence of electronic wave from the viewpoint that an eigenstate arises as a result of self-interference of a moving electron. Numerical results for a Hénon–Heiles potential in which chaotic motion can occur in the classical mechanics indicate that electronic eigenstates can arise even when motion of an electron is non-periodic. The results show that, in the quantum mechanics, periodicity is unnecessary for the formation of eigenstates. 相似文献
77.
The photoelectron spectrum of the dichromium oxide cluster anion, Cr2O-, and the analysis by the density-functional theory revealed that the spins of the two Cr atoms in Cr2O- are ferromagnetically coupled, and that its total spin magnetic moment is as large as 9 mu(B). This ferromagnetic spin coupling is induced by oxidation; the mixing of Cr 3d with O 2p orbitals plays an important role in a spin coupling between the localized electrons at the two Cr sites bridged by the O atom. The present finding is in marked contrast to the pure chromium dimer, which is known to be antiferromagnetic due to the strong sextuple Cr-Cr bond. 相似文献
78.
[reaction: see text] An intermolecular cobalt-phosphine-catalyzed Diels-Alder reaction of piperine is described. The dimerization of piperine in the presence of cobalt-phosphine complexes gave much better yields than that in the presence of only cobalt, which, combined with the result under the purely thermal conditions, indicates that addition of phosphine ligands changes the inhibition of cobalt to the reaction into promotion. For elucidation of the distinction, different cobalt-catalyzed mechanisms were proposed for the Diels-Alder dimerization of piperine. 相似文献
79.
Water-loaded poly(1,4-piperazinediylterephthaloyl) (PPiP) microcapsules were prepared by an interfacial polycondensation technique using piperazine and terephthaloyl dichloride as water-soluble and water-insoluble monomers, respectively. The organic solvents used were mixtures of cyclohexane and chloroform and n-hexane and chloroform in various volume ratios. The microcapsules obtained were washed successively with n-hexane, acetone, and water and fractionated into several fractions of different sizes. A suspension of each fraction and a solution of sodium chloride were mixed and the change with time in electroconductivity of the mixture was measured to estimate the rate of salt entry into the microcapsules. The permeability coefficient for the salt was calculated from the rate of salt entry. It was found that the permeability increased as the capsule size increased and was higher for the capsules prepared with n-hexane—chloroform mixtures than for those prepared with cyclohexane—chloroform mixtures. These findings were explained in terms of the density and thickness of the capsule membrane. 相似文献
80.
Summary The coagulation of ferric oxide sol by several organic solvents, such as ethyl alcohol, has been studied. It has been observed
that the coagulation takes place when the dielectric constant of medium is lowered to a certain critical value for coagulation
by the addition of any organic solvent. The lowering of dielectric constant of medium is accompanied by the contraction of
electrical double layer around sol particle, which leads to coagulation.
With 1 figure and I table 相似文献
Zusammenfassung Koagulation eines Ferrioxidsols durch verschiedene organische L?sungsmittel findet statt, wenn die Dielektrizit?tskonstante bis auf einen „kritischen” Wert durch Zufügung irgendeines organischen L?sungsmittels vermindert wird. Die Erniedrigung der DK des Mediums bedingt die Kontraktion der elektrischen Doppelschichten der Solpartikel, so da? Koagulation erfolgt.
With 1 figure and I table 相似文献