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441.
Brus J 《Solid state nuclear magnetic resonance》2000,16(3):151-160
Intense sample heating through high-speed magic-angle spinning (MAS; up to 58 K temperature difference) is demonstrated. The role of probehead and spinner design, as well as that of the temperature of the bearing air on the heating of a rotating sample, is examined. MAS-induced heating can affect the accurate determination of the isotropic value of the chemical shift as well as the principal values, asymmetry and anisotropy parameters of the chemical shift tensor. In some cases, a very large temperature gradient (12 K) within the fast rotating sample was found, which may limit the resolution of high-speed 1H MAS nuclear magnetic resonance (NMR) spectra. 相似文献
442.
From solid state NMR spectra, a lower shielding of poly(ethylene oxide) (PEO) protons, in contrast to higher shielding of PEO carbons, has been found for PEO/hydroxybenzene and PEO/LiCF3SO3 complexes in comparison with neat PEO. The same PEO chemical shifts were found both for crystalline and amorphous phase of PEO/LiCF3SO3 polymer electrolyte, confirming the same interaction in both phases. Measurements of 2D 1H CRAMPS exchange NMR spectra have been used to characterize proton distances in complexes of PEO and benzene derivatives. A close contact (∼ 0.3 nm) between aromatic and PEO protons was detected in some cases. From the measurements of the cross polarization 1H → 13C, using Lee-Goldburg irradiation of 1H nuclei, the distance between LiCF3SO3 carbon and the nearest PEO protons in the PEO/LiCF3SO3 complex was determined. 相似文献
443.
Time dependence of the gel formation in toluene solutions of polycarbonate (PC) was investigated by two-dimensional Fourier-transform infrared (2D FT-IR) correlation spectroscopy. The 2D correlation approach reveals that there are at least three bands in the C=O stretching region. The intensity increase of the band at 1771 cm−1 occurs later compared with the onset of the intensity changes of the bands at 1778 and 1765 cm−1 corresponding to amorphous and crystalline-like domains, respectively. The band at 1771 cm−1 is assigned to the chain conformations occurring in the partial-order regions accompanying crystalline-like domains. Splitting of the signals of aromatic carbons in the solid-state 13C CP/MAS NMR spectra of semicrystalline PC and PC-PEO blends indicates restricted mobility resulting from the fixed ordering due to partial crystallinity of PC itself and from blending of PC with PEO. The decreasing mobility of PC with the increasing content of highly mobile PEO in the blends was proved by the dipolar dephasing rates obtained in the 1H-1H CRAMPS (combined rotation and multi-pulse spectroscopy) NMR experiments. 相似文献
444.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option. 相似文献
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