Diffusion of Methylaluminoxane (MAO) in Toluene Probed by1H NMR Spin-Lattice Relaxation Time

Hansen, Eddy W.; Blom, Richard; Kvernberg, Per Olav

doi:10.1002/1521-3935(20011001)202:14<2880::aid-macp2880>3.0.co;2-x

Cited by 25 publications

(8 citation statements)

References 8 publications

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“…However, even though MAO has been used as catalyst activator for decades, its complete structure as well as the exact mechanism of activation remain incompletely defined . Molecular weight depends on the measurements, − typically ranging from 1000 to 2000 Da, with an average composition of (Me 1.4–1.5 AlO 0.75–0.8 ) n . Various spectroscopic investigations and quantum mechanical calculations indicate that the general molecular formula is best written as (MeAlO) x (Me 3 Al) y , where x is the degree of oligomerization the MAO cluster achieves during its synthesis via hydrolysis of trimethylaluminum (TMA), and y is the number of TMA monomers which are incorporated into the clusters, either as Me 2 AlO n groups ( n = 1,2) or as datively bound Me 3 Al. − …”

Section: Introductionmentioning

confidence: 99%

Oxidation of Methylalumoxane Oligomers: A Theoretical Study Guided by Mass Spectrometry

et al. 2018

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Methylalumoxane (MAO) plays a critical role in catalytic polymerization of olefins, both as activator of the precatalyst and scavenger of impurities. The latter involves oxidation of MAO, which is not well understood at a molecular level. On the basis of our previous computational explorations of the structure of MAO and electrospray ionization mass spectrometry (ESI-MS) studies of its oxidation, we report here a systematic theoretical study to shed light on the oxidation process. We identify the structural features of the MAO that are essential for oxidation by screening the thermodynamics of the oxidation reactions as a function of shape and size of the previously justified model MAOs. In correlation with previously reported ESI-MS studies of the corresponding anions (Chem.

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Section: Introductionmentioning

confidence: 99%

Oxidation of Methylalumoxane Oligomers: A Theoretical Study Guided by Mass Spectrometry

et al. 2018

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“…[27][28][29][30] Size estimates of MAO vary from around 10 up to 200 Al atoms per molecule, [31,32] with diameters up to 20 . [11,33] Because MAO is likely a mixture of different species, it would be highly desirable to gain a proper understanding of the structural characteristics and chemical compositions of the species that are formed during its preparation. This information would be particularly important from the point of view of catalyst development, because it may be that only species with certain types of chemical environments can take part in the catalyst-activation process, as suggested by the need for a large excess of MAO to activate the pre-catalysts.…”

Section: Introductionmentioning

confidence: 99%

Screening the Thermodynamics of Trimethylaluminum‐Hydrolysis Products and Their Co‐Catalytic Performance in Olefin‐Polymerization Catalysis

Linnolahti

Laine

Pakkanen

2013

Chemistry A European J

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Herein, we introduce an approach for the computational screening of stoichiometric reactions between trimethylaluminum (TMA) and water. The thermodynamic products of these reactions are methylaluminoxanes (MAOs) with different compositions, which have the general formula (AlOMe)n(AlMe3 )m, in which n describes the degree of oligomerization and m is the number of associated TMA molecules. These reaction products were thoroughly explored up to n=4, thus demonstrating the thermodynamically preferable association of up to four AlMe3 molecules, that is, TMA molecules in their monomeric form. The relative Lewis acidities of the Al sites in these MAOs were systematically explored and we found that the associated TMA molecules were a key ingredient for co-catalytic activity in olefin-polymerization catalysis. This conclusion was supported by computational studies on catalyst activation, which revealed an exergonic insertion of ethene into the metallocene/MAO complex.

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“…The catalyst activity decreased at higher TMA/MAO ratio. 13 To improve above results, we examined the 1 H-NMR study of an MAO solution and in situ reaction of BADB and an MAO solution 14 and the spectra are shown in Figure 1.…”

Section: Resultsmentioning

confidence: 99%

Ethylene polymerization using (n-BuCp)2ZrCl2 catalyst activated with a cross-linked MAO-supported cocatalyst

Yoon

2004

Macromol. Res.

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A new type of cross-linked methylaluminoxane (MAO)-supported cocatalyst has been prepared by the reaction of a soluble MAO and a cross-liking agent such as an aromatic diamine compound. The cross-linked MAO-supported cocatalyst was used for the polymerization of ethylene in the presence of bis(n-butylcyclopentadienyl) zirconium dichloride, (n-BuCp) 2 ZrCl 2 . The catalyst activity of (n-BuCp) 2 ZrCl 2 cocatalyzed with the new supported cocatalyst was higher than that of the commercial silica-supported MAO (SMAO) cocatalyst. The molecular weight and the bulk density of the polyethylene produced by using the new supported cocatalyst were slightly higher than those of polyethylene synthesized using commercial SMAO. The resulting polyethylene particles possess spherical morphologies with very few fine particles.

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Diffusion of Methylaluminoxane (MAO) in Toluene Probed by1H NMR Spin-Lattice Relaxation Time

Cited by 25 publications

References 8 publications

Oxidation of Methylalumoxane Oligomers: A Theoretical Study Guided by Mass Spectrometry

Oxidation of Methylalumoxane Oligomers: A Theoretical Study Guided by Mass Spectrometry

Screening the Thermodynamics of Trimethylaluminum‐Hydrolysis Products and Their Co‐Catalytic Performance in Olefin‐Polymerization Catalysis

Ethylene polymerization using (n-BuCp)2ZrCl2 catalyst activated with a cross-linked MAO-supported cocatalyst

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