Ethylene polymerizations, highly active

One of the more extraordinary recent developments in nickel and palladium polyalkene catalysis has been the development of a-diimines with bulky substituents as ligands in nickel and palladium complexes. When bulky aryl groups are used (R = isopropyl), these catalysts polymerize ethylene with high activities to high molecular weight highly branched... 

Polystyrene supported (arylmido)vanadium(V) complex 22 was prepared and tested for its catalytic activity for ethylene polymerization. The activity seemed to be improving by the polystyrene support probably due to the improved stability of the catalytically-active species (leading to the enhancement of its lifetime, and the productivity of the supported catalyst), and the resultant polymer by 22 possessed high molecular weight with unimodal distribution (A/ - = 4.9). fhe activity drastically... 

Although actinide complexes usually disqualify themselves from industrial utility by their radioactivity, the thorocene (C5(CH3)5)2Th(CH3)2 displays high activity for ethylene polymerization after activation (101). Like zirconocenes, this family of metallocenes tends to remain on the +4 manifold, and thus requires ionization by an appropriate cocatalyst (in this case, a highly Lewis acidic surface such as dehydroxylated alumina or MgCl2) before it is active. 

The cationic group 4 metallocenes are 14-electron cf complexes, and the alkyl species accept coordination of an olefin and allow its insertion into the metal-carbon bond (Scheme 2). The coordination site for monomers switches alternately, and it is important for an understanding of stereoselective polymerization. Highly active metallocene catalysts allow more than 1000 ethylene insertions per second at one catalyst molecule. 

Most chromium-based catalysts are activated in the beginning of a polymerization reaction through exposure to ethylene at high temperature. The activation step can be accelerated with carbon monoxide. Phillips catalysts operate at 85—110°C (38,40), and exhibit very high activity, from 3 to 10 kg HDPE per g of catalyst (300—1000 kg HDPE/g Cr). Molecular weights and MWDs of the resins are controlled primarily by two factors, the reaction temperature and the composition and preparation procedure of the catalyst (38,39). Phillips catalysts produce HDPE with a MJM ratio of about 6—12 and MFR values of 90—120. 

Recently some information became available on a new type of highly active one-component ethylene polymerization catalyst. This catalyst is prepared by supporting organometallic compounds of transition metals containing different types of organic ligands [e.g. benzyl compounds of titanium and zirconium 9a, 132), 7r-allyl compounds of various transition metals 8, 9a, 133), 7r-arene 134, 185) and 71-cyclopentadienyl 9, 136) complexes of chromium]. 

Nickel(II) complexes of ligands 38 (R=H,Me R =H,Me,Et,Tr,CH30 R =H, CH3O R =H, F, CH3O) are highly active catalysts for ethylene polymerization [86,159], whereas palladium(II) complexes possess catalytic properties in the copolymerization of CO and alkenes [160] (Scheme 36). 

On the other hand, the polymer prepared by the embedded catalyst shows T around 130 °C, which is a typical melting temperature of high density polyethylene. There was little activity difference between the polyethylene produced by embedded particles and those by homogeneous catalysts. The results of ethylene polymerization using embedded catalyst and homogeneous catalyst are summarized in Table 1 and Fig. 2,... 

Thus, in the presence of methylaluminoxane (MAO) at 23°C, (C5H5B-N(/-Pr)2)2 ZrCl2 polymerizes ethylene with an activity of 105 kg ofpolyethylene/(h [Zr] mol), similar to that observed with well-studied Cp2ZrCl2 as the catalyst. It is believed that MAO is functioning in its usual role in these Ziegler-Natta polymerizations (methylation of Zr and abstraction of methyl to form a highly reactive Zr cation).41... 

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