- Ethylene polymerization reactions with multicenter Ziegler-Natta catalysts-manipulation of active center distribution
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This article describes ethylene/1-hexene copolymerization reactions with a supported titanium-based, multicenter Ziegler-Natta catalyst. The catalyst was modified by pretreating its solid precursor with AlEt2Cl and with similar organoaluminum chlorides, Al2Et3Cl3, AlEtCl2, and AlMe2Cl. Testing of the untreated and the pretreated catalysts in copolymerization reactions under standard reaction conditions demonstrated that the modifying agents produce two changes in the catalyst. First, the pretreatment significantly reduces the reactivity of active centers that produce high molecular weight, highly crystalline copolymer components with a low 1-hexene content. Second, the pretreatment noticeably increases the reactivity of active centers that produce low molecular weight copolymer components with a high 1-hexene content. The first effect is caused by Lewis acidbase interactions of the modifiers with the active centers, whereas the second (activating) effect is due to the removal of catalyst poisons (organosilicon compounds generated in the process of the catalyst synthesis) by AlEt2Cl.
- Kissin, Yury V.,Mink, Robert I.
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- Selective Formation of Alkoxychlorosilanes and Organotrialkoxysilane with Four Different Substituents by Intermolecular Exchange Reaction
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Alkoxychlorosilanes are scientifically and industrially important toward preparing silicone and silica as well as preparation of siloxane-based nanomaterials by stepwise reactions of Si?OR (R=alkyl) and Si?Cl groups. Intermolecular exchange of alkoxy and chloro groups between alkoxysilanes and chlorosilanes (functional group exchange reaction) provides an efficient and environmentally benign route to alkoxychlorosilanes. BiCl3 as a Lewis acid catalyst can promote the functional group exchange reactions more efficiently than conventional acid catalysts. Higher reactivity has been observed for chlorosilanes with smaller numbers of Si?CH3 groups and for alkoxysilanes with larger numbers of Si?CH3 groups. The reaction mechanism is proposed and selective syntheses of alkoxychlorosilanes are demonstrated. These findings also enable us to synthesize an organotrialkoxysilane with four different substituents.
- Komata, Yuma,Yoshikawa, Masashi,Tamura, Yasuhiro,Wada, Hiroaki,Shimojima, Atsushi,Kuroda, Kazuyuki
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p. 3225 - 3233
(2016/11/29)
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- Synthesis, structure, immobilization and solid-state NMR of new dppp- and tripod-type chelate linkers
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Chelating phosphines incorporating ethoxysilane functions for immobilizations have been synthesized and fully characterized. (EtO)Si(CH 2PPh2)3, (EtO)2Si(CH 2PPh2)2, and Si(CH2PPh 2)4 could be prepared in high yields from cheap starting materials. The ethoxysilanes, as well as a Pd complex thereof have been characterized by X-ray structures, and immobilized on silica. The success of the immobilization was proved by 31P solid-state NMR of the dry materials and of the suspensions. Two representative chelate metal complexes, (EtO)2Si(CH2PPh2)2PdCl2 and (EtO)Si(CH2PPh2)3W(CO)3 have been synthesized, characterized and immobilized.
- Bogza, Mona,Oeser, Thomas,Blümel, Janet
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p. 3383 - 3389
(2007/10/03)
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- Exchange reactions in alkoxy derivatives of silicon and germanium
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Reaction SiCl4+ Ge(OR)4 → GeCl4+ Si(OR)4 was carried out for the first time. Triethoxysilane reduces tetraethoxygermane via intermediate formation of unstable GeH(OEt)3 that transforms into GeO·Et2O or Ge(OH)2.
- Chernyshev,Belyakova,Knyazev,Turkel'Taub',Ovsyankina,Ugarova,Yakovleva
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p. 650 - 652
(2007/10/03)
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- Recovery of trimethylchlorosilane from its azeotropic mixture with SiCl4
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Reaction of tetraethoxysilane with the azeotropic mixture Me3SiCl-SiCl4 in the presence of certain cyclic (tetrahydrofuran, dioxane) and acyclic (diethyl ether) ethers, ethanol, or dimethylformamide was studied with the aim of SiMe3Cl recovery.
- Voronkov,Baryshok,Kuznetsova
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p. 2091 - 2094
(2007/10/03)
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- Synthesis and reactivity of bis(triethoxysilyl)methane, tris(triethoxysilyl)methane and some derivatives
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Syntheses of new poly(trifunctional-silyl)alkanes, which are potent coupling agents of hybrid organic-inorganic materials have been thoroughly examined. Optimization of the Benkeser reaction using chloroform, trichlorosilane and tri-n-butylamine (respective ratios 1:4.5:3) afforded bis(trichlorosilyl)methane isolated as bis(triethoxysilyl)methane after ethanolysis (overall yield 60%). With nine equivalents of trichlorosilane, tris(trichlorosilyl)methane is preferentially formed, isolated as tris(triethoxysilyl)methane (30% yield). C-Substituted bis(triethoxysilyl) methanes were obtained after metallation of the α-carbon and trapping experiments with the corresponding alkyl halides. In the case of tris(triethoxysilyl)carbanion, only MeI and Br2 were able to give the anticipated products. Unexpectedly, CO2 insertion afforded the stable ketene, [(EtO)3Si]2C=C=O.
- Corriu, Robert J.P.,Granier, Michel,Lanneau, Gerard F.
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