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排序方式: 共有172条查询结果,搜索用时 15 毫秒
51.
Seyed Heidar Mirjahanmardi Faramarz Afshar Taromi Roya Zahedi Mehdi Nekoomanesh Haghighi Roghayeh Jamjah Gholamali Jafari Asl 《Polymer Science Series B》2016,58(6):619-628
The multi-ether compounds with different numbers of methoxy groups containing 1,3-dimethoxy-2,2-bis(methoxymethyl)propane and 1-methoxy-2,2-bis(methoxymethyl)butane were synthesized using the Williamson reaction from pentaerythritol and 1,1,1-tris(hydroxymethyl)propane, respectively, in the presence of sodium hydride and methyl iodide in tetrahydrofuran and they were characterized by 1H NMR, 13C NMR, and FTIR spectroscopy. These compounds were employed as external donors in the polymerization of propylene using the industrial Ziegler-Natta catalyst. A commercial spherical MgCl2-supported Ziegler-Natta catalyst containing diisobutyl phthalate as the internal donor was used for the polymerization of propylene. The role of ether compounds and industrial alkoxysilanes on the properties of polypropylene were studied using the xylene solubility method, melt flow index, gel permeation chromatography, scanning electron microscopy, and differential scanning calorimetry. The addition of the electron donors has led to improvements in the activity and selectivity of the Ziegler-Natta catalyst system. 相似文献
52.
Effect of fiber geometry on macroscale friction of ordered low-density polyethylene nanofiber arrays
Lee DH Kim Y Fearing RS Maboudian R 《Langmuir : the ACS journal of surfaces and colloids》2011,27(17):11008-11016
Ordered low-density polyethylene (LDPE) nanofiber arrays are fabricated from silicon nanowire (SiNW) templates synthesized by a simple wet-chemical process based on metal-assisted electroless etching combined with colloidal lithography. The geometrical effect of nanofibrillar structures on their macroscale friction is investigated over a wide range of diameters and lengths under the same fiber density. The optimum geometry for contacting a smooth glass surface is presented with discussions on the compromise between fiber tip-contact area and fiber compliance. A friction design map is developed, which shows that the theoretical optimum design condition agrees well with the LDPE nanofiber geometries exhibiting high measured friction. 相似文献
53.
Moallemi Bahmani Maryam Haji Shabani Ali Mohammad Dadfarnia Shayessteh Afsharipour Roya 《Journal of fluorescence》2022,32(4):1337-1346
Journal of Fluorescence - In this study, a sensitive fluorimetric method is proposed for the determination of piroxicam using nitrogen graphene quantum dots (N-GQDs) and gold nanoparticles coated... 相似文献
54.
Gholamhossein Rounaghi Massoumeh Mohajeri Zahra Atashi Roya Mohammadzadeh kakhki 《Journal of inclusion phenomena and macrocyclic chemistry》2012,73(1-4):435-441
The stability constants (Kf) for the complexation reactions of Cr3+, Mn2+ and Zn2+ metal cations with macrocyclic ligand, 15-crown-5 (15C5), in acetonitrile (AN), ethanol (EtOH) and also in their binary solutions (AN–EtOH) were determined at different temperatures, using conductometric method. 15C5 forms 1:1 complexes with Cr3+, Mn2+ and Zn2+ cations in solutions. A non-linear behaviour was observed for changes of logKf of the metal ion complexes versus the composition of the mixed solvent. The order of stability of the metal–ion complexes in pure AN and in a binary solution of AN–EtOH (mol% AN?=?52) at 25?°C was found to be: (15C5Zn)2+?>?(15C5·Mn)2+?>?(15C5·Cr)3+, but in the case of pure EtOH at the same temperature, it changes to: (15C5·Zn)2+?>?(15C5·Cr)3+?>?(15C5·Mn)2+. The results also show that the stability sequence of the complexes in the other binary solutions of AN–EtOH (mol% AN?=?26 and mol% AN?=?76) varies in order: (15C5·Cr)3+?~?(15C5·Zn)2+?>?(15C5·Mn)2+. The values of the standard thermodynamic quantities (ΔHC°, ΔSC°) for formation of (15C15-Cr3+), (15C5-Mn2+) and (15C5-Zn2+) complexes were obtained from the temperature dependence of the stability constants and the results show that the thermodynamics of complexation reactions is affected by nature and composition of the solvent systems and in most solution systems, the complexes are enthalpy stabilized but entropy destabilized. 相似文献
55.
A new application of the Mukaiyama reagent for the simple phosphine-free conversion of alcohols into the corresponding alkyl thiocyanates is described. This transformation can be achieved either in acetonitrile or under solvent-free conditions and the products obtained in good to excellent yields. The solvent-free procedure described here is the first report on the solvent-free thiocyanation of alcohols. 相似文献
56.
An efficient approach for the synthesis of novel 1,3-indandionylamidinium betaines via four-component reaction of 1,3-indandione, aldehydes, amines, and isocyanides, without assistance of any catalyst and under mild reaction conditions has been reported. The structures of these compounds were confirmed by IR, mass spectroscopic, 1H NMR, 13C NMR, and single-crystal X-ray diffraction studies. 相似文献
57.
A sequential (R)-BINAP·AgIF (2,2′-bis(diphenylphosphino)-1,1′-binaphthyl) (6–10 mol %), and (Ph3P)2PdIICl2 (bis(triphenylphosphine)palladium(II) dichloride) (2 mol %) catalyzed asymmetric Sakurai–Hosomi–Yamamoto allylation/Mizoroki–Heck reaction that affords C1-chiral 3-methylene-indan-1-ols with enantiomeric excess (ee) up to 80% is reported. Notably, this protocol allows for the use of various o-substituted benzaldehydes and allyltrimethoxysilane. It was also discovered that the presence of electron-rich groups had no effect on the enantioselectivity of the reaction, whereas electron-withdrawing groups lead to erosion in product ee. 相似文献
58.
Ali Reza Kiasat Roya Mirzajani Haji Shalbaf Tahereh Tabatabaei Mehdi Fallah‐Mehrjardi 《中国化学会会志》2009,56(3):594-599
A facile synthesis of 1,2‐azidoalcohols from their epoxides using α,α',α”‐N‐hexakis(triethylammoniummethylene chloride)‐melamine as a multi‐site phase‐transfer catalyst in water was developed. By this eco‐friendly and highly atom‐economic method, a variety of 1,2‐azidoalcohols was obtained in high yields with excellent regioselectivity and in short reaction times. Application of this six‐site PTC in the ring opening of epoxides by cyanide, acetate and chloride anions was also studied. The catalyst can be recovered after completion of the reaction and can be recycled without affecting the catalytic property. 相似文献
59.
Complete palladium nanoshells were prepared by reducing palladium ions in a one-step reaction onto preformed silica cores
of ca. 90 nm, which had been coated with successive layers of poly(diallyldimethyl ammonium chloride), poly(sodium styrenesulfonate)
and finally poly(diallyldimethyl ammonium chloride) to reverse the zeta potential of the silica cores. This constitutes the
first reported method for complete palladium nanoshell formation without the use of other metals as nucleation sites. The
morphology of the nanoshell is of the rough discrete particle type rather than the smooth continuous type. 相似文献
60.
Xin Bin Roya Momen Tianlv Xu Steven R. Kirk Michael Filatov Samantha Jenkins 《International journal of quantum chemistry》2019,119(11):e25903
A balanced treatment of the covalent and ionic contributions to the ground and excited states originating from torsion about double bonds is known to be strongly dependent on the presence of dynamic electron correlation. We undertake an analysis of the minimum energy pathways corresponding to deactivation of the first excited singlet state of PSB3. In doing so we consider torsion about the three double bonds including other intramolecular degrees of freedom, such as the bond length alternation. The 3-D bond-path analysis provides a new ‘bond-localized orbital-like’ directional interpretation of bonding. Therefore, we present a more sophisticated method of determination of the degree of covalent and ionic contributions known to be responsible for altering the relative stability of the S1/S0 conical intersections. The results presented suggest that the commonly used simplified multi-reference methodologies that often result in incorrect predictions for the excited state deactivation reaction mechanism. 相似文献