摘要:

AbstractThe reactions of tetraalkyldialumoxanes (R2Al‐O‐AlR2)nor alkylalumoxane (AlOR)nwith acetylacetone, some electron donors (ethers, amines, nitriles) and alcohols were discussed. The structures of alumoxanes were also considered. Despite a lot of studies the structure is not always clear and changes with a change of many parameters such as kind of ligands, synthetic conditions (solvents, reaction temperature, molar ratio of reactants), methods of isolation

ISSN:1022-1360    

DOI:10.1002/masy.19950970103

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe isolation of non‐fluxional alumoxane compounds, [(tBu)2Al{OAl(tBu)2}]2and [(tBu)AlO]n(n = 6, 7, 8, 9), has allowed for an investigation of the mode of activity observed for alumoxanes as co‐catalysts for the zirconocene polymerization of olefins. [(tBu)2Al{OAl(tBu)2}]2, which contains two three‐coordinate aluminum centers, shows no reaction with Cp2ZrMe2, and no catalytic activity towards ethylene polymerization. In contrast, the closed cage compound [(tBu)AlO]6reacts reversibly to give the ion pair complex, [Cp2ZrMe][(rBu)6Al6O6Me], which is active as a catalyst for the polymerization of ethylene. Polymerization is also observed for mixtures of Cp2ZrMe2with [(tBu)AlO]n(n = 7, 9). A new concept, “latent Lewis acidity”, is proposed to account for the reactivity of the cage alumoxanes, [(

ISSN:1022-1360    

DOI:10.1002/masy.19950970104

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractMethylaluminoxane prepared from trimethylaluminium on a surface of ice mainly can be described as [Al4O3(CH3)6]4. This is shown through analysis, phase separation experiments with diethyl ether and molecular weight determinations in benzene, 1, 4‐dioxane, tetrahydrofuran and trimethylaluminium. It is discussed that the reason for forming this ball‐like structure is the saturation of four coordinated Al4O3(CH3)6. This molecule has a cavern which contains a solvent molecule or a molecule of trimethylaluminium. The consequences for the formation of the catalytically active structure together with metallocene are discus

ISSN:1022-1360    

DOI:10.1002/masy.19950970105

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe synthetic methods of heterogeneous metallocene catalysts reported so far in academic journals are summarized together with their catalyst performance. Some of our new results in this field are also described in brief.

ISSN:1022-1360    

DOI:10.1002/masy.19950970106

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA short review of the fundamental investigations in the fields of synthesis, properties and application of alumoxanes for the last thirties years is given.

ISSN:1022-1360    

DOI:10.1002/masy.19950970107

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe optimal ratio of Al/Zr in Metallocene/Methylalumoxane catalysts lies between 5000 to 10000. Bimetallic deactivation reactions and equilibria are responsible for this high excess. Substitution at the cyclopentadienyl or indenyl ligands can decrease the possibility for a hydrogen transfer and deactivation resulting in higher activity, higher molecular weights of the polymers and less excess of MAO. The MAO/metallocene ratio can also be reduced by supporting the metallocene on silica.

ISSN:1022-1360    

DOI:10.1002/masy.19950970108

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractUltraviolet/visible (UV/VIS) spectroscopic investigation of the reaction between tungsten oxytetrachloride and methylalumoxane (MAO) respectively trimethylaluminum (TMA) resulted in a method for the determination of the amount of “free” TMA in MAO samples. The development of the method of investigation is descri

ISSN:1022-1360    

DOI:10.1002/masy.19950970109

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA study of the reactions of Cp2Ti13CH3CI and Cp2Ti(CH3)2with AIMe3(TMA) and/or methylaluminoxane (MAO) and of the13C 90% enriched ethylene polymerization in situ in the presence of the same catalytic systems has been made by13C NMR spectroscopy. The NMR data have been compared with the catalytic activity. Active cation‐like species such as Cp2TiMe+CI·[AIMeO]n−and Cp2TiMe+Me·[AIMeO]n−and side products have been identified. The role of “free” and “associated” AIMe3, contained in MAO solutions, has

ISSN:1022-1360    

DOI:10.1002/masy.19950970110

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractTwo types of copolymerizations were found with the catalyst system Cp2ZrCl2/MAO. One was a less exothermic reaction, and another was a more exothermic one. The former provided a polymer with a single composition distribution because of a single cationic active site. The latter provided a polymer with a bimodal composition distribution, indicating the existence of two active sites. The two active sites were investigated through the comparison of MAO systems and alkylaluminium / borate systems. We speculated that the two active sites were the normal cationic site and the active site where the interaction between a cationic metallocene and an aluminium compound was strong.

ISSN:1022-1360    

DOI:10.1002/masy.19950970111

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe controlled hydrolysis of trimethylaluminium (TMA) on a defined surface of cooled ice to the corresponding aluminoxanes provides good yields of a toluene soluble product. The reaction was conducted in a specially designed reactor with a rotating scraper. The product properties are independent of reaction temperature between −28 and −40 °C and scraping speed, but can be varied with the extent of hydrolysis.A series of reactors was built for the investigation of this reaction system, the biggest ones producing between 0.5 and 1 kg of aluminoxane solution per day. The safety and ease of use was improved with each subsequent reactor de

ISSN:1022-1360    

DOI:10.1002/masy.19950970112

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY