Metallocenes methyl aluminoxane

Naga, N. Shiono, T. Ikeda, T. Copolymerization of propene and nonconjugated diene involving intramolecular cychzation with metallocene/methyl aluminoxane. Macromolecules 1999, 32, 1348-1355. 

It is now well recognised that the active species is a cationic complex, or more precisely a solvent-separated or tight ion pair, the structure of which depends on the mode of catalyst activation. Early spectroscopic and synthetic studies on metallocene dimethyl precursors helped to outline the principal reaction pathways, these have been reviewed [16, 21, 23]. Some of this chemistry is briefly summarised here since it presents the background for the understanding of later studies on methyl-aluminoxane (MAO) systems. 

Asymmetric synthesis cyclopolymerization of 1,5-pentadiene (261) was performed with an optically active metallocene catalyst. The polymer (262) obtained by (S)-ethylenebis(tet-rahydroindenyl)zirconium (S)-binaphtholate ([a] 435+1848°) in the presence of methyl aluminoxane (MAO) showed molecular rotation [(p] 4os-49.3°, and NMR analysis showed that the polymer had -68% tram structure. An optically active copolymer consisting of cyclic 262 units and linear units formed by 1,2-insertion shows LC phases. ... 

Some support materials can be rendered Lewis acidic enough to ionize dialkyl metallocenes. Marks and co-workers have reported (33) that alnmina dried at very high temperatures can react at least to some small degree with both thorium-and zirconium-based metallocene dimethyl species to yield active catalysts for polyethylene. The resulting cationic metal center is believed to remain coordinated to the surface through an Al-O-M Lewis acid/base linkage, at least prior to exposure to ethylene. Hybrid surface/cocatalyst systems based on aluminum alkyl-treated clays have been developed (34) in which the solid substrate appears to play some role in promoting polymerization activity far beyond that expected for non-methyl aluminoxane- or trialkylaluminum-activated catalysts. 

Brookhart et al. [57,58] described square planar nickel and palladium-diimine systems which are capable of polymerizing ethene to high molecular weight polymers with activities comparable to the metallocene catalyst systems when activated with methyl-aluminoxane. 

In the 1980s Sinn, Kaminsky, and coworkers found that metallocenes such as Cp2ZrCl2 and Cp2ZrMc2 in conjugation with methyl aluminoxane, which is obtained from trimethyl aluminum and water, polymerize ethylene with activities exceeding 25 X lO gPE/gZrhatm [4]. A polymer thus obtained showed controlled MWD and comonomer incorporation, because all the active sites behave in the same way... 

Propylene-1-butene and propylene-1-pentene copolymerization at 60°C in the propylene bulk with the homogeneous isospecific metallocene catalyst of the symmetry rac-Me2Si(4-Ph-2-MeInd)2ZrCl2 activated by methyl-aluminoxane is studied. Thermal, mechanical characteristics, and thermooxidation stability have been investigated. 

In this study, we examined the copolymerization of propylene with 1-butene and 1-pentene in liquid propylene medium in the presence of a highly active isospecific homogeneous a 5o-metallocene catalyst with the C -symmetry, rac-Me2Si(4-Ph-2-MeInd)2ZrCl2, activated by methyl-aluminoxane (MAO). The effects of the type of comonomer on the rate of copolymerization and the molecular mass characteristics, microstructure, thermophysical, and mechanical properties of the copolymers are investigated. The results of this study are compared with the data obtained with the same system used for the copolymerization of propylene with ethylene, 1-hexene, and l-octene. ... 

Syndiotactic polystyrene (SPS) can be readily polymerized using homogeneous or heterogeneous metallocene catalysts, based on group 4 metal compounds, especially titanium compounds like T1CI4, CpTiClj, and Cp Ti(OCH3)3 with methyl aluminoxane (MAO) as cocatalyst [1-3]. The recent developments of transition metal catalysts and reaction mechanisms are discussed in earlier chapters. This chapter will be focused on the quantitative aspects of SPS polymerization kinetics and related physical and chemical phenomena. 

As mentioned earlier, the presence of trace quantities of water enhances the activity of the Cp TiCl - plus AlMCj-based catalytic system enormously. It turns out that partial hydrolysis of AlMCj leads to the formation of methyl aluminoxanes (MAOs) according to reaction 6.5.1.1. The actual cocatalyst in this type of metallocene or half-metallocene-based catalytic systems is therefore MAO. 

Metallocene are group IV metals (Tj, Zr, Hf, and Rf, but commonly Zr is used) complexed with cyclopentadiene and can be activated by methyl aluminoxane (MAO) as follows ... 

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