Aluminum methylalumoxane

The polymerization of methyl methacrylate (MMA) by Cu(ll) amidinate complexes (Scheme 222) in combination with alkyl aluminum complexes has been reported. The preferred alkylating agent is methylalumoxane (MAO) in... 

The isolation and structural characterization of aluminum hydroxides with terminal OH groups is a s)mthetic challenge, and efforts were made to prepare well-defined analogues of methylalumoxane (MAO). The strategy of hydrolysis of metal chlorides in the presence of a base to quench the hydrogen chloride generated during the reaction was adopted. This synthesis can be performed in two different ways (i) hydrolysis of a metal halide in a two-phase liquid NHs-toluene system in the presence of KOH and KH and (ii) hydrolysis of a metal halide in the presence of a stoichiometric amount of N-heterocyclic carbene. Both routes are reliable, but the latter one may prove to offer more versatility and be relatively easier to conceive. 

Recently the authors invented another efficient, immobilized methylalumoxane cocatalyst partially hydrolyzed trimethylaluminum (PHT) that proved to be different from common methylalumoxanes. As a partial crystalline solid, PHT exhibits an octahedral environment for the aluminum atoms. PHT can be... 

Methylalumoxane (MAO) activated 6fa(cyclopentadienyl)zirconium dimethyl Alumoxide and trimethyl aluminum, and 6w(cyclopentadienyl)titanium diphenyl Methylalumoxane and his(cyclopentadienyl)zirconium dichloride... 

Tactic PS. Isotactic (iPS) and syndiotactic (sPS) PSs can be obtained by the polymerization of styrene with stereospecific catalysts of the Ziegler-Natta-type. Aluminum-activated TiCls yields iPS while soluble Ti complexes [eg, ( j -CsHslTiCls] in combination with a partially hydrolyzed alkylaluminum [eg, methylalumoxane] yield sPS. The discovery of the sPS catalyst system was first reported in 1986 (33). As a result of the regular tactic structure, both iPS (phenyl groups cis) and sPS (phenyl groups alternating trans) are highly crystalline. Samples of iPS quenched from the melt are amorphous, but become... 

The role of methylalumoxane (MAO) as a cocatalyst to activate zirconocene compounds such as Cp ZrCl to create a single-site ethylene polymerization catalyst is similar, in some respects, to the role simple aluminum alkyls (AlRj) play in activating Ziegler catalysts. For example, MAO acts as an alkylating agent to form the initial Zr-carbon bond (Zr-CH ) necessary to initiate the polymerization process. However, experimental evidence obtained by a variety of methods clearly has shown that the MAO reacts with the zirconium center to form a zirconium cation of the type [CpjZr-CHS] in which the zirconium is not reduced to a lower oxidation state, but remains as a d° metal and Zr(IV) oxidation state. The MAO, therefore, forms an anion moiety to complete the ion pair necessary to create the active species, as illustrated in Equation 4.1. 

As briefly mentioned above, some prior work on alucones has been reported. One distinguishing feature of this class of materials, in contrast to their relatives the alumoxanes, is the presence of not only aluminum and oxygen atoms in the network backbone, but carbon atoms as well. Examples given in the U. S. Borax technical reports (Figs. 1 - 3) demonstrate this incumbent feature. Alumoxanes, and in particular methylalumoxane (MAO), lack this salient organic component of the polymer frame (10). Their basic repeat unit is f(R)Al-<5x9 however, it is known now that such a simplistic formula is not representative of the magnitude of the components present in such compositions. Ra er, clusters built up with Al-0-A1 linkages are observed in MAO (11). 

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