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951.
Structural phase transition at 290 K and the implication on the intermediate phase above 290 K in powdered RbMnCl3 are observed by using a solid-state 87Rb NMR spectroscopy. Quadrupole coupling constants (e2qQ/h), the asymmetry parameters (η), and the relative peak intensities for two physically nonequivalent Rb sites, Rb(I) and Rb(II), are determined from nonlinear least-squares fits to the 87Rb NMR powder patterns in the temperature range from 260 to 330 K. Quadrupole coupling constants and the asymmetry parameters are examined for the detection of the phase transition resulting in a significant structural change in the Rb(II) site. In addition, changes in the relative peak intensity between the Rb(I) and Rb(II) sites seem to suggest the existence of an anomalous intermediate phase, which is complemented by the differential scanning calorimetry and X-ray diffraction studies. 相似文献
952.
If Tφ is a hyponormal Toeplitz operator with polynomial symbol φ = ḡ + f (f, g ∈ H∞ (𝕋 )) such that g divides f, and if ψ := then where μ is the leading coefficient of ψ and 𝒵(ψ) denotes the set of zeros of ψ. In this paper we present a necessary and sufficient condition for Tφ to be hyponormal when φ enjoys an extremal case in the above inequality, that is, equality holds in the above inequality. 相似文献
953.
The cure behavior, thermal stability, and mechanical properties of diglycidylether of bisphenol A (DGEBA)/polysulfone (PSF) blends initiated by 1 wt % N‐benzylpyrazinium hexafluoroantimonate as a cationic latent catalyst were investigated. The DGEBA/PSF content was varied within 100/0–100/40 wt %. Latent properties were studied through the measurement of the conversion as a function of the curing temperature, and the cure activation energy (Ea) was studied by the Kissinger method with a dynamic differential scanning calorimetry analysis. The thermal stabilities, largely based on the integral procedural decomposition temperature (IPDT) and decomposed activation energy (Et), were investigated by the measurement of thermogravimetric analysis. For the mechanical properties of the casting specimens, the critical stress intensity factor (KIC) test was performed, and their fractured surfaces were examined with scanning electron microscopy. Ea, IPDT, Et, and KIC increased with PSF increasing in the neat epoxy resin up to 30 wt %. However, there was a marginal decrease in the blend system in both the thermal and mechanical properties due to the phase separation between DGEBA and PSF. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 121–128, 2001 相似文献
954.
Young Gun Ko Ung Su Choi Tai Young Kim Dong June Ahn Yong Jin Chun 《Macromolecular rapid communications》2002,23(9):535-539
A new chelating fiber, poly(acrylo‐amidino diethylenediamine), was synthesized based on polyacrylonitrile fibers in diethylenetriamine with the aid of AlCl3. Complex formation with CrO42– was strongly pH‐dependent, as complexes formed only in the presence of NH3+ and NH2+. In the medium pH region, both ionic and hydrogen bonds were formed between poly(acrylo‐amidino diethylenediamine) and the chromate ion, as was confirmed by means of FT‐IR spectroscopy. 相似文献
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957.
SangNyon Kim SangChul Shim DoYoung Kim YoungHa Rhee YoungBaek Kim 《Macromolecular rapid communications》2001,22(13):1066-1071
Biodegradable poly(3‐hydroxyundecenoate) (PHU) films on silicon wafers were crosslinked with UV light under patterned masks. The films were crosslinked most efficiently when irradiated in the presence of diphenyl(2,4,6‐trimethylbenzoylphosphane oxide) as the initiator. Crosslinked patterns were developed with depolymerase solution because crosslinked PHU was degraded much more slowly than natural PHU. Patterned images with thicknesses of as low as 2.5 μm were obtained showing the potential application of PHU in microlithography as a photosensitive material, which is friendly to the environment. 相似文献
958.
Young Gun Ko Ung Su Choi Byeng Gil Ahn Dong June Ahn 《Journal of polymer science. Part A, Polymer chemistry》2000,38(15):2815-2823
High‐performance materials for flameproofing, phosphates (polyphosphate and ammonium phosphate) were synthesized on viscose rayon felt. This surface reaction has the advantage of a nonblooming effect and an application in thermosetting plastics. Metal complexes have the effect of reducing the amount of smoke. Therefore, in the second step, transition‐metal complexes were synthesized on the viscose rayon ammonium phosphate felt. This article focuses on the surface modification of phosphates and metal complexes on viscose rayon. All reactions were confirmed by attenuated total reflectance Fourier transform infrared and time‐of‐flight secondary ion mass spectrometry. As the concentrations of phosphoric acid and urea increased, the peak intensities of ammonium ion groups and phosphate groups greatly increased. The thermal properties of the synthesized materials were studied with thermogravimetric analysis and oxygen index testing. On the basis of the experimental results, the synthesized flame‐retardancy materials showed excellent physicochemical and thermal effects and flame retardancy. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2815–2823, 2000 相似文献
959.
Yong Seok Lee Young Chan Bae 《Journal of polymer science. Part A, Polymer chemistry》2000,38(22):4128-4136
A new model has been proposed that takes into account the specific interaction between nematic liquid crystal and polymer. A generalized lattice fluid model was employed to describe the specific interaction between liquid crystal and polymer. The proposed model postulates that a specific interaction between dissimilar components in a mixture has both an energetic and an entropic component. A degeneracy parameter and an interaction parameter are also discussed, followed by a comparison of the experimental data to the model. The results show that that a specific interaction plays an important role in the phase behaviors of the given systems. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4128–4136, 2000 相似文献
960.