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Metallocene Complexes (metallocene + complex)
Selected AbstractsDimethylsilylbis(1-indenyl) zirconium dichloride/methylaluminoxane catalyst supported on nanosized silica for propylene polymerizationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2008Kuo-Tseng Li Abstract A dimethylsilylene-bridged metallocene complex, (CH3)2Si(Ind)2ZrCl2, was supported on a nanosized silica particle, whose surface area was mostly external. The resulting catalyst was used to catalyze the polymerization of propylene to polypropylene. Under identical reaction conditions, a nanosized catalyst exhibited much better polymerization activity than a microsized catalyst. At the optimum polymerization temperature of 55°C, the former had 80% higher activity than the latter. In addition, the nanosized catalyst produced a polymer with a greater molecular weight, a narrower molecular weight distribution, and a higher melting point in comparison with the microsized catalyst. The nanosized catalyst's superiority was ascribed to the higher monomer concentration at its external active sites (which were free from internal diffusion resistance) and was also attributed to its much larger surface area. Electron microscopy results showed that the nanosized catalyst produced polymer particles of similar sizes and shapes, indicating that each nanosized catalyst particle had uniform polymerization activity. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Synthesis and Dynamic Features of (Chloro)zirconocene Cations Stabilised by Pendant (Diarylphosphanyl)alkyl and (Dimethylamino)alkyl Substituents at Their Cyclopentadienyl Ring SystemsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2003Steve Döring Abstract Treatment of the substituted (diarylphosphanyl)methyl group-4 metallocene complexes [(C5H4,CR1R2,PAr2)2ZrCl2] (2: R1/R2 = CH3/CH3, H/CH3, H/aryl) with Li[B(C6F5)4] in dichloromethane solution results in chloride ligand abstraction (with LiCl precipitation) to yield the complexes [(C5H4,CR1R2,PAr2)2Zr,Cl+] (5), with both phosphanyl groups internally coordinated to the metal centre. Three possible diastereoisomers are observed in the case of 5c (R1 = H; R2 = CH3), while bulkier R2 substituents give higher selectivities. The thermally induced (reversible) cleavage of the Zr,phosphane linkage results in dynamic NMR behaviour. Gibbs activation energies of ,G,(298 K) = 14.8 ± 0.5 and 14.5 ± 0.5 kcal/mol were obtained for these intramolecular equilibration processes in the complexes trans - 5d (R1 = H; R2 = Ph) and trans - 5e (R1 = H; R2 = ferrocenyl), respectively. Treatment of the substituted (dimethylamino)methyl metallocene complexes [(C5H4,CR1R2,NMe2)2ZrCl2] (6a, 6b) with Li[B(C6F5)4] proceeds analogously to yield the cation systems [{C5H4,C(CH3)2,NMe2}2ZrCl+] (12a) and [{C5H4,CH(CH3),NMe2}2ZrCl+] (12b, three possible diastereoisomers). Both complexes have their pairs of amino groups coordinated to the metal centre. The complexes exhibit dynamic NMR spectra. Selective equilibration of the diastereotopic N(CH3)A(CH3)B resonances of complex 12a is observed [,G,(233 K) = 11.5 ± 0.2 kcal/mol], whereas the adjacent C(CH3)A(CH3)B methyl groups remain diastereotopic. The dynamic equilibration of the latter was observed at a markedly higher temperature [,G,(333 K) = 17.3 ± 0.2 kcal/mol]. Treatment of [{C5H4,C(CH3)2,NMe2}CpZrCl2] (10) with Li[B(C6F5)4] resulted in the formation of complex [{C5H4,C(CH3)2,NMe2}CpZr,Cl+] (11), which shows the internal ,N(CH3)A(CH)B equilibration proceeding with a markedly higher activation barrier [,G,(333 K) = 17.6 ± 0.2 kcal/mol] than in 12a, and a stereochemical memory effect indicative of solvent coordination to the metal centre of the resulting highly electrophilic chlorozirconocene cation intermediate. Complex 11 was characterised by an X-ray crystal structure analysis, which shows the internal Zr,amine coordination. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Stereoregular P(MMA)-clay nanocomposites by metallocene catalysts: In situ synthesis and stereocomplex formationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2007Wesley R. Mariott Abstract This contribution reports the synthesis and characterization of stereochemically controlled, as well as crystalline stereocomplex, P(MMA)-clay nanocomposites using metallocene complexes and alane-intercalated clay activators. The ligand elimination and exchange reactions involving Lewis acids E(C6F5)3 (E = Al, B) and an organically modified montmorillonite clay were employed to synthesize the alane-intercalated clay activators. When combined with dimethyl metallocenes of various symmetries, these clay activators brought about efficient MMA polymerizations leading to in situ polymerized, stereochemically controlled P(MMA)-intercalated clay nanocomposites. The most noticeable thermal property enhancement observed for the clay nanocomposite P(MMA), when compared with the pristine P(MMA) having similar molecular weight and stereomicrostructure, has a considerable increase in Tg (,10 °C). Mixing of dilute THF solutions of two diastereomeric nanocomposites in a 1:2 isotactic to syndiotactic ratio, followed by reprecipitation or crystallization procedures, yielded unique double-stranded helical stereocomplex P(MMA)-clay nanocomposites with a predominantly exfoliated clay morphology. Remarkably, the resulting crystalline stereocomplex P(MMA) matrix is resistant to the boiling-THF extraction and its clay nanocomposites exhibit high Tm of 201 to 210 °C. Furthermore, the stereocomplex P(MMA)-clay nanocomposite shows a one-step, narrow decomposition temperature window and a single, high maximum rate decomposition temperature of 377 °C. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2581,2592, 2007 [source] Al(OH)3 - and AlO(OH)-based cocatalysts for metallocene complexes in alkene polymerization reactionsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2005Yury V. Kissin Alternative cocatalysts for metallocene complexes: combinations of AlMe3 and one of the two inorganic aluminum compounds, Al(OH)3 and AlO(OH). [source] Novel intramolecular coordination chemistry of some new metallocene complexesCHINESE JOURNAL OF CHEMISTRY, Issue 11 2001Yan-Long Qian Abstract The metabolic thermogenic curves of liver mitochondria isolated from the livers of Cyprinus Carpio vol and its parents were determined at 28°C by using an LKB-2277 Bioactivity Monitor. The results indicated that their thermogenic curves are different The total heat output and total time of the metabolism of the liver mitochondria of the hybrid F1 (Cyprinus Carpio val) are more than those of its parents, and its maximum heat power is between that of the female parent and male parent. The relationship between their metabolic thermogenic curves and character of mitochondrial metabolism, and thermokinetics and the heterosis were analyzed and discussed. The character of the mitochondrial thermogenic curves reflected the physiologic character of heterosis. The microcalorimetric method proved to be a probable and sensitive tool for the assessment of heterosis. [source] | |||||||||||||