排序方式: 共有4条查询结果,搜索用时 15 毫秒
1
1.
A. N. Panin T. A. Sukhova N. M. Bravaya 《Journal of polymer science. Part A, Polymer chemistry》2001,39(11):1901-1914
Ethylene polymerizations with catalytic systems Me2SiCp*NtBuZrX2 ( 1 ) [Cp* = C5(CH3)4; X = Cl ( 1Cl ), Me ( 1Me )], triisobutylaluminum (TIBA), perfluorophenylborate CatB(C6F5)4 [Cat = CPh3 ( 3 ), Me2NHPh ( 4 )], or Me2SiCp2ZrX2 [X = Cl ( 2Cl ), Me ( 2Me )]/TIBA/ 3 ( 4 ) were performed within a wide range of ethylene pressures of different Al/Zr ratios, and Zr/B = 1. Catalytic systems 1Cl ( 2Cl )/TIBA/ 3 led to the formation of very high linear molecular weight polyethylene (PE) of Mη ∼2,000,000 with low activity. The replacement of both chlorine ligands in the precatalyst for the methyl ones led to the formation of active species producing low molecular weight PE with high activity. Chain transfer to ethylene was shown to be the main reaction controlling PE chain propagation: kp/ktr ∼20–30 for 1Me /TIBA/ 3 and kp/ktr ∼350–500 for 2Me /TIBA/ 3 . It was suggested that TIBA was present in the active center first in the form of a neutral heterobimetallic Zr–Al bridged complex followed by the formation of a partially polarized Zr–Al(Cl)R2 (R = iBu) or an unreactive Zr–AlR3 cationic complex by abstraction of the alkyl ligand under the action of borate. It was concluded that AlR3 from the latter cationic complex may be easily reversibly replaced under the specific coordination of ethylene or accumulated α-olefin, giving rise to highly labile and sterically accessible cationic species. Experiments on ethylene polymerization with the catalytic systems 1Cl ( 1Me )/TIBA/ 3 /Ph2NH, 1Cl ( 1Me )/TIBA/ 4, 2Cl ( 2Me )/TIBA/ 3 /Ph2NH, and 2Cl ( 2Me )/TIBA/ 4 were performed to confirm the suggestion. Catalytic systems derived from dichloride complexes in the presence of a σ-donor substrate also produced low molecular weight PEs with molecular weight characteristics similar to those of products obtained with the dimethylated precatalysts. The specific feature of active species derived from 2Me complexes to isomerize coordinated α-olefin into trans-vinylene polymer chains was also revealed. The catalytic behavior of the ternary catalytic system based on 2Me relative to 2Me or 2Cl precatalysts activated with polymethylaluminoxane at different Al/Zr ratios was compared. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1901–1914, 2001 相似文献
2.
A. N. Panin Z. M. Dzhabieva P. M. Nedorezova V. I. Tsvetkova S. L. Saratovskikh O. N. Babkina N. M. Bravaya 《Journal of polymer science. Part A, Polymer chemistry》2001,39(11):1915-1930
An investigation of the catalytic behavior of the dimethylated zirconocenes Me2SiCp*NtBuZrMe2 [Cp* = C5(CH3)4; 1Me ], Me2SiCp2ZrMe2 ( 2Me ), Cp2ZrMe2 ( 3Me ), Ind2ZrMe2 ( 4Me ), Me2SiInd2ZrMe2 ( 5Me ), Et(2-MeInd)2ZrMe2 ( 6Me ), and Me2Si(2-MeInd)2ZrMe2 ( 7Me ) with the combined activator triisobutylaluminum (TIBA)/CPh3B(C6F5)4 (Al/Zr = 250; B/Zr = 1) in ethylene polymerizations at increased monomer pressures (5–11 bar, 30 °C) was carried out. Sterically opened zirconocenes in ternary catalysts gave rise to active species effective in the formation of low molecular weight polyethylenes (PEs). These active species tended to increase the PE molecular weight [ 1Me (2100) < 2Me (20,000) < 5Me (89,000) < 3Me (94,500)] under similar conditions. PE obtained with 4Me showed a bimodal gel permeation chromatography curve with a 64% peak area [weight-average molecular weight (Mw) = 43,000] and a 36% peak area (Mw = 255,000). The increase in sterical demands from the zirconocenes was also demonstrated by the reduction of the chain transfer to monomer, the reinsertion of vinyl-ended PE chains, and their ability for isomerization. These reactions were most pronounced for the zirconocenes 1Me and 2Me . The active species responsible for the formation of low molecular weight PEs deactivated quickly. The zirconocenes 6Me , 7Me , and (2-PhInd)2ZrMe2 ( 8Me ) bearing substituent at the 2-position of the indenyl ring was activated with TIBA alone, yielding active species effective in ethylene and propylene polymerizations. PEs formed with 6Me – 8Me complexes activated with TIBA had high molecular weights. An increase in the Al/Zr ratio in the catalytic system 8Me /TIBA from 50 to 300 led to an enhancement of the molecular weight of polypropylene (PP) samples from oligomeric products to an viscosity-average molecular weight of 220,000. The increase in the molecular weights of PPs with an increase in the propylene concentration was also observed. An analysis of the catalytic performance of the 8Me /TIBA system showed first-order dependency of the initial polymerization rates on the TIBA concentration and close to second-order dependency on propylene. The second-order dependency on the monomer concentration is explained in terms of the monomer participation in the initiation step of the polymerization reaction. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1915–1930, 2001 相似文献
3.
Kazuo Soga Eiichi Kaji Toshiya Uozumi 《Journal of polymer science. Part A, Polymer chemistry》1998,36(1):129-135
Several kinds of dichlorobis(β-diketonato)titanium complexes, i.e., Ti(ace-tylacetonato)2Cl2, Ti(1-benzoylacetonato)2Cl2, Ti(2,2,6,6-tetramethyl-3,5-heptanedionato)2Cl2 and Ti(4,4,4-trifluoro-1-phenyl-1,3-butanedionato)2Cl2, were synthesized and the corresponding MgCl2-supported catalysts were prepared by impregnation method. The test of them for propene polymerization revealed that those MgCl2-supported catalysts could be activated not only by methylaluminoxane (MAO) but also by ordinary alkylaluminums as well. The effect of typical Lewis bases on the catalyst performance was investigated in some detail, which indicated that organic silanes are most effective for the improvement of isospecificity of those catalysts. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 129–135, 1998 相似文献
4.
1