排序方式: 共有42条查询结果,搜索用时 15 毫秒
1.
An efficient and simple synthesis of α‐hydroxyphosphonates via reaction of aldehydes and ketones with dimethylphosphite in the presence of MgCl2/Et3N base system is reported. The use of readily available and easy to handle reagent MgCl2/Et3N makes this method simple, convenient, and practical. 相似文献
2.
David Ribour Vincent Monteil Roger Spitz 《Journal of polymer science. Part A, Polymer chemistry》2008,46(16):5461-5470
Thermal treatments under vacuum of conventional supported Ziegler‐Natta precatalysts (MgCl2/TiCl4/Dibutylphthalate) were conducted to gradually remove titanium to modify the active sites distribution. Only limited detitanations of precatalysts were achieved paying attention not to chemically alter the internal donor (T < 150 °C). Used in combination with the required cocatalyst and external donor in the propylene slurry polymerization, the modified precatalysts exhibited a drop of activity versus decreasing titanium content but the distributed polymer properties are almost not affected (a slight narrowing of molecular weight distribution was observed). After a titanium chloride secondary impregnation (possibly done in presence of an additional Lewis base), activity resumed but polymer properties are once again unchanged. These findings highlight the difficulty to separate the different families of active sites and lead us to propose a cluster organization of titanium active sites. Active sites are composed of titanium clusters having a size distribution at the precatalyst surface, possessing a critical operating size and operating collectively in polymerization. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5461–5470, 2008 相似文献
3.
Tatiana B. Mikenas Vladimir A. Zakharov Lyudmila G. Echevskaya Mikhail A. Matsko 《Journal of polymer science. Part A, Polymer chemistry》2007,45(22):5057-5066
The effects of polymerization temperature, polymerization time, ethylene and hydrogen concentration, and effect of comonomers (hexene‐1, propylene) on the activity of supported catalyst of composition LFeCl2/MgCl2‐Al(i‐Bu)3 (L = 2,6‐bis[1‐(2,6‐dimethylphenylimino)ethyl] pyridyl) and polymer characteristics (molecular weight (MW), molecular‐weight distribution (MWD), molecular structure) have been studied. Effective activation energy of ethylene polymerization over LFeCl2/MgCl2‐Al(i‐Bu)3 has a value typical of supported Ziegler–Natta catalysts (11.9 kcal/mol). The polymerization reaction is of the first order with respect to monomer at the ethylene concentration >0.2 mol/L. Addition of small amounts of hydrogen (9–17%) significantly increases the activity; however, further increase in hydrogen concentration decreases the activity. The IRS and DSC analysis of PE indicates that catalyst LFeCl2/MgCl2‐Al(i‐Bu)3 has a very low copolymerizing ability toward propylene and hexene‐1. MW and MWD of PE produced over these catalysts depend on the polymerization time, ethylene and hexene‐1 concentration. The activation effect of hydrogen and other kinetic features of ethylene polymerization over supported catalysts based on the Fe (II) complexes are discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5057–5066, 2007 相似文献
4.
Tatiana B. Mikenas Vladimir A. Zakharov Lyudmila G. Echevskaya Michail A. Matsko 《Journal of polymer science. Part A, Polymer chemistry》2005,43(10):2128-2133
Data on ethylene polymerization over supported LFeCl2/MgCl2 catalysts {L = 2,6‐bis[1‐(2,6‐dimethylphenylimino)ethyl]pyridyl} containing AlR3 (R = Me, Et, i‐Bu, or n‐Oct) as an activator are presented. These catalysts are highly active (100–300 kg of polyethylene/g of Fe h bar of C2H4) and stable in ethylene polymerization at 70–80 °C. Data on the effects of the iron content, AlR3 type, Al(i‐Bu)3 concentration, and hydrogen presence on the catalyst activity are presented. The molecular structure of polyethylene produced with these catalysts (including the molecular masses, molecular mass distribution, branching, and number of C?C bonds) has been studied; data on the effects of AlR3 and hydrogen on the molecular structure are presented. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2128–2133, 2005 相似文献
5.
The series of calculations of the potential energy curves of the diatomic radicals MeIIX (MeII = second group metal, X = halogen), has been extended to MgCl, CaF and CaCl. The calculations have been performed according to a stepwise procedure, outlined in previous works. The presently available results allow comparisons for the first members of the series. 相似文献
6.
Polypropylene (PP) has become an indispensable material in our daily lives. Annual worldwide production of PP is now more than 30000000 tons and is predicted to grow at an annual rate of about 6% during the first decade of the 21st century. Commercial production of PP began in 1957 with the use of TiCl(3) catalysts established by Ziegler and Natta. However, the low activities and low stereospecificities of the catalysts resulted in large amounts of catalyst residue and atactic PP in the product, necessitating steps for their removal in commercial production. As a means of finding appropriate catalysts, we developed MgCl(2)-supported TiCl(4) catalysts, which basic concept was introduction of organic compounds onto the inorganic crystal catalyst surface. This addition led to remarkable enhancements in stereospecificity with extremely high activity. Use of the new catalysts enlarged and simplified the PP production process by eliminating the steps previously required for removal of catalyst residue and atactic PP. In addition, it greatly improved the properties of the PP, enabling a much wider range of PP applications by replacing metal and engineering plastics with the highly stereoregular PP. Therefore, these catalysts helped the rapid establishment of the current PP industry and now play a major role in production. The latest MgCl(2)-supported TiCl(4) catalyst is providing precise control of the isotactic PP structure. Future expectations for this type of catalyst are to acquire a single-site nature and to contribute to the creation of a new class of hybrid materials. 相似文献
7.
MgCl_2晶型对丙烯聚合MgCl_2载体催化剂活性的影响张明辉,肖世镜中国科学院化学研究所,北京,10080)关键词丙烯聚合、MgCl2、载体催化剂近年来,有关MgCI。载体催化剂的研究报道和综述文章不少,但涉及载体晶型对催化剂结构性能的影响却少见.... 相似文献
8.
9.
给电子体在丙烯聚合MgCl2载体催化剂体系中的作用 总被引:5,自引:0,他引:5
制备了3种含有不同内给电子体(邻苯二甲酸二异丁酯,9,9-二甲氧基甲基-芴和1,1-双甲氧基甲基-环丁烷)的MgCl2负载型丙烯聚合齐格勒-纳塔(Z-N)催化剂,研究了给电子体结构与聚合性能之间的关系,用红外光谱剖析了催化剂及其相关化合物的结构,结果发现催化剂中的内给电子体直接与MgCl2配位,而没有与TiCl4结合.内给电子体的加入,降低了Z-N催化剂中钛的含量,提高催化丙烯聚合的活性,使聚合物的分子量分布变窄.聚合物立构规整度的变化强烈依赖于内给电子体的结构. 相似文献
10.
Effect of different donors on kinetics of Zn catalysts and molecular weight of the obtained polypropylene 总被引:2,自引:0,他引:2
María Lujn Ferreira Daniel E. Damiani 《Journal of molecular catalysis. A, Chemical》1999,150(1-2):53-69
This paper studies MgCl2/internal donor/TiCl4//external donor/AlEt3 catalytic systems where ethyl benzoate (E.B.) or 2,2,6,6 tetramethylpiperidine (TMPiP) are used as internal and external donors. E.B. as external donor does not change the molecular weight of the product with TMPiP as internal donor. The molecular weight of polypropylene decreases drastically and global productivity and stereoselectivity are very low with MgCl2/internal Donor/TiCl4//external donor/AlEt3 when TMPiP is the external and internal donor. In this case the insoluble fraction in n-heptane is highly stereospecific and the molecular weight is similar to commercial products. We present a new explanation of these results, based on Ystenes proposal, comparing both precatalysts. 相似文献