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排序方式: 共有240条查询结果,搜索用时 358 毫秒
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Takeaki Miyamoto Yukiko Sato Toru Shibata Mitsuhiko Tanahashi Hiroshi Inagaki 《Journal of polymer science. Part A, Polymer chemistry》1985,23(5):1373-1381
The degree of substitution (DS) and distribution of O-acetyl groups of water-soluble cellulose acetate (CA) were investigated by 13C-NMR. For this purpose, three different series of CA samples with low DS were prepared by respective homogeneous reaction, i.e., (1) deacetylation of cellulose triacetate (CTA) in acetic acid—water solution (D-series), (2) reaction of CTA with hydrazine (H-series), and (3) acetylation of cellulose with acetic anhydride in a 10% LiCl-dimethylacetamide solution (A-series). It was found that (i) water-soluble CA can be obtained only from D-series products, (ii) the DS value of water-soluble CA ranges from 0.5 to 1.1, (iii) the D-series products exhibit little difference between the relative DS values at C-2, C-3 and C-6 hydroxyl groups, and (iv) the relative DS at C-6 hydroxyl groups is very high compared to those at C-2 and C-3 hydroxyl groups in H- and A-series products. Aqueous solution of water-soluble CA (D-series sample) showed no gel—sol transition, even when the temperature was raised to 95°C. X-ray diffraction observations revealed that the water-soluble D-series samples were essentially noncrystalline, but the water-insoluble A-series samples were crystalline. It was also found that the relative ease of acetylation is C-6 > C-2 > C-3. 相似文献
64.
A tandem quadrupole mass spectrometer is used to study the charge transfer reactions NH3+ + NO and NO+ + NH3 over a collision energy range 1.5–13 eV. The vibrational state of the reagent ions is selected by resonance-enhanced multiphoton ionization. For the 0.9 eV exothermic process NH3+ + NO → NH3 + NO+ excitation of the v2 umbrella bending mode (v2 = 0–12) causes no marked change in the charge transfer cross section, while in the reverse process NO+ + NH3 → NO + NH3+ excitation of the NO+ vibration (v = 0–6) strongly enhanced the charge transfer cross section. 相似文献
65.
Takimiya K Konda Y Ebata H Niihara N Otsubo T 《The Journal of organic chemistry》2005,70(25):10569-10571
[reaction, structures: see text] A general and convenient synthesis of benzo[1,2-b:4,5-b']dichalcogenophenes including the thiophene (BDT, 1), selenophene (BDS, 2), and tellurophene (BDTe, 3) homologues is developed. Thus synthesized heterocycles are structurally characterized by single-crystal X-ray analysis, and all three homologues are isostructural with one another. They all have completely planar molecular structures packed in a herringbone arrangement. Their physicochemical properties were also elucidated by means of cyclic voltammetry (CV) and UV-vis spectra. 相似文献
66.
Makino K Nakajima T Shikamura M Ito F Ando S Kochi C Inagawa H Soma G Terada H 《Colloids and surfaces. B, Biointerfaces》2004,36(1):35-42
Monodispersed PLGA microspheres containing rifampicin (RFP) have been prepared by solvent evaporation method using a Shirasu porous glass (SPG) membrane. The microspheres were spherical and their average diameter was about 2 microm. The loading efficiency of rifampicin was dependent on the molecular weight of PLGA. The higher loading efficiency was obtained by the usage of PLGA with the lower molecular weight, which may be caused by the interaction of the amino groups of rifampicin with the terminal carboxyl groups of PLGA. PLGA with the monomer compositions of 50/50 and 75/25, of lactic acid/glycolic acid, were used in this study. From rifampicin-loaded PLGA microspheres formulated using PLGA with the molecular weight of 20,000, rifampicin was released with almost constant rate for 20 days after the lag phase was observed for the initial 7 days at pH 7.4. On the other hand, from rifampicin-loaded PLGA microspheres formulated using PLGA with the molecular weight of 5000 or 10,000, almost 90% of rifampicin-loaded in the microspheres was released in the initial 10 days. Highly effective delivery of rifampicin to alveolar macrophages was observed by the usage of rifampicin-loaded PLGA microspheres. Almost 19 times higher concentration of rifampicin was found to be incorporated in alveolar macrophages when rifampicin-loaded PLGA microspheres were added to the cell culture medium than when rifampicin solution was added. 相似文献
67.
The polymerization of 1,3-butadiene (BD) was carried out in the presence of a catalyst composed of neodymium 2-ethylhexanoate, triisobutyl aluminum, diisobutyl aluminum hydride (DIBAH), ethylaluminum sesquichloride and acetylacetone. The molecular weight of the BR could be controlled with DIBAH. The reactive polymer was then chemically modified with styreneoxide (STO). The STO content of BR increased with the decrease in the molecular weight of the BR. This polymer was modified by the STO at the chain terminal end. The physical properties of the vulcanizates with the modified BR were measured. The abrasion resistance and the tensile strength were found to be improved. 相似文献
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