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981.
982.
Young Jin Cho Seung Hwan Lee Jong Woo Bae Sung Hoon Kim Sam Rok Keum Cheol Min Yoon 《合成通讯》2013,43(12):2205-2211
The 7-acetoxyspiropyrans (4a and 4b) have been prepared by the reaction of Fischer's bases (3) with 2,4-diacetoxybenzaldehyde in refluxing ethanol in moderate yields. The acetyl group of 7-acetoxy-spiropyran 4a was easily removed to give a 7-hydroxyspiropyran 6 in high yield under the basic condition. 相似文献
983.
We study the Ricci dark energy model (RDE) which was introduced as an alternative to the holographic dark energy model. We
point out that an accelerating phase of the RDE is that of a constant dark energy model. This implies that the RDE is not
a new model of explaining the present accelerating universe. 相似文献
984.
Jobi Kodiyan Varghese Dong Sik Park Jong Yeob Jeon Bun Yeoul Lee 《Journal of polymer science. Part A, Polymer chemistry》2013,51(22):4811-4818
Simple mixing of H3Co(CN)6 and ZnCl2 in methanol resulted in precipitates of [ZnCl]+2[HCo(CN)6]2?, constituting a new type of double metal cyanide (DMC) catalyst exhibiting a high performance in carbon dioxide (CO2)/propylene oxide (PO) copolymerization. High‐molecular‐weight poly(propylene carbonate‐co‐propylene oxide)s [poly(PC‐co‐PO)s] (Mn~40,000) were consistently obtained with high carbonate fractions (~60 mol %) and a high selectivity (>95%) with the new type of DMC catalyst. Conventional preparation of the DMC catalyst using K3Co(CN)6 and ZnCl2 required removing KCl through thorough washing and resulted in lower carbonate fractions (10–40 mol %), which depended on the washing conditions. Feeding hydrophobic diols such as 1,10‐decanediol as chain transfer agent preserved the high carbonate fraction (~60%) and enabled precise control of the molecular weight, including preparation of a low‐molecular‐weight poly(PC‐co‐PO)‐diol (Mn ~2000), which was a flowing viscous liquid with a low Tg (?30 °C) suitable for polyurethane applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4811–4818 相似文献
985.
986.
Kyong Nam Kim Jong Hyeuk Lim Geun Young Yeom 《Plasma Chemistry and Plasma Processing》2010,30(1):183-190
Plasma and electrical characteristics of an internal-type inductively coupled plasma source with a Ni–Zn ferrite module installed
near the antenna were investigated for different rf power frequencies of 2 and 13.56 MHz. Due to the lower heating of the
Ni–Zn ferrite module on the antenna for the operation at 2 MHz compared to the operation at 13.56 MHz, higher plasma density
and lower rf rms antenna voltage were resulted for the operation at 2 MHz in addition to more stable plasma characteristics.
By the application of 500 W of rf power to the source, a high plasma density of 8 × 1011 cm−3 which is about four times higher than that with 13.56 MHz could be obtained at the pressure of 10 mTorr Ar. When photoresist
etch uniformity was measured for the operation with 2 MHz by etching photoresist on a 300 mm diameter substrate using 10 mTorr
Ar/O2 (9:1) mixture, the etch uniformity of about 5.5% could be obtained. 相似文献
987.
Myunghun Kim Chang Kook Hong Soona Choe Sang Eun Shim 《Journal of polymer science. Part A, Polymer chemistry》2007,45(19):4413-4420
Multiwalled carbon nanotubes (MWNTs) were effectively functionalized with KMnO4 in the presence of a phase‐transfer catalyst at room temperature. The hydroxyl functionalized MWNTs were reacted with a vinyl‐group carrying silane‐coupling agent and the terminal vinyl groups were used to fabricate polystyrene (PS) brushes by solution polymerization. Finally, PS‐encapsulated MWNTs were obtained. The synthesis results were verified from FT‐Raman, thermal gravimetric analysis, energy dispersive X‐ray analysis, and transmission electron microscope. PS‐encapsulated MWNTs had much improved dispersion stability in hydrophobic medium, toluene since grafted hydrophobic PS interacts with media and has improved compatibility. This functionalization technique would provide a facile route to prepare various polymer brushes on the surface of MWNTs to improve the dispersion of MWNTs for potential applications. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4413–4420, 2007 相似文献
988.
Yeong‐Soon Gal Sung‐Ho Jin Jong‐Wook Park 《Journal of polymer science. Part A, Polymer chemistry》2007,45(23):5679-5685
A new ionic polyacetylene with two aromatic heterocycles (pyridyl and thienyl) was prepared by the activation polymerization of 2‐ethynylpyridine by using 3‐(6‐bromohexyloxy)methylthiophene without any additional initiator or catalyst. The activated acetylenic triple bond of N‐substituted‐2‐ethynylpyridinium bromide, formed at first quaternarization process, was susceptible to linear polymerization. The instrumental analysis data on the polymer structure revealed that the polymer have the conjugated polyene backbone structure with the designed two aromatic heterocycles. The photoluminescence peak is located at 510 nm corresponding to a photon energy of 2.43eV. The electrochemical properties of this ionic polyacetylene were also measured and discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5679–5685, 2007 相似文献
989.
990.
Three new 2-picolyloxy lariat ether compounds are prepared and solid-state structures are determined for two of them. Complexation behavior for a series of lariat ethers with pyridyl-containing side arms toward alkali metal cations and Ag+ is assessed by two-phase metal picrate extraction from aqueous solutions into chloroform and in homogeneous solutions by isothermal titration calorimetry in methanol. 相似文献