Ethylene polymerizations, highly active molecular catalysts

Discovery of Highly Active Molecular Catalysts for Ethylene Polymerization... 

Description Liquid or gaseous ethylene is fed, together with a solvent and required comonomer(s) into a stirred, liquid-filled, vessel-type reactor (1). The reactor is operated adiabatically thus, the feed is precooled. All heat of reaction is used to raise polymerization temperature up to approximately 200°C. Hydrogen is used to control polymer molecular weight. A high-activity, proprietaiy catalyst is prepared onsite from commercially available components. Ethylene... 

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... 

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. 

The first examples of highly active olefin polymerization catalysts based on late transition metals were nickel and palladium complexes containing bulky diimine ligands.310 312 For example, complex (120) was found to polymerize ethylene with an activity of ll,000gmmol h bar A range of PE materials with molecular weights up to 106 and... 

When less bulky ancillary ligands are used /3-hydride elimination leads to the formation of Q-olefins. As a consequence iminopyridine complexes are typically much less active than the diimine catalysts and afford lower-molecular-weight PE.321-324 For example, MAO/(122) polymerizes ethylene to branched oligomers with Mn < 600, and 240 branches per 1,000 carbons.325 Complex (123), is highly active for ethylene polymerization (820gmmol 1 h bar ).326 As with the diimine systems, reduction in the steric bulk of the ligand substituents results in reduced activity and lower-molecular-weight products. 

Conversely, Ti-FI catalysts with MAO normally show lower (but still high) ethylene polymerization activities and form higher molecular weight PEs relative to the Zr congeners. The ethylene polymerization activities of Ti-FI catalysts were also... 

After activation with MAO (molar ratios [Al] [Zr] = 1000) the polymerization of ethylene has been successfully carried out using the zirconocene functionalized dendrimer at 40 bar ethylene pressure and 70 °C. We obtained high activity and productivity values for the ethylene polymerization and polymers with very high molecular masses in the range of 2 x 10 g/mol. The polydispersity of the polymer is quite low (3.0) indicating the single site character of the catalytically active species. Optimization of this system and study of the mechanism are stiU under investigation. Nevertheless, these preliminary results reveal the suitability of polyphenylene dendrimers as supports for zirconocene catalysts. 

Covalently attaching molecular catalysts to supports is a method that can minimize catalyst leaching. In 1998, a PS-supported titanocene was prepared by Barrett and de Miguel, which displayed 41 g-PE mmol-Ti h of activity. Soga and co-workers reported a series of poly(siloxane)-supported metallocene catalysts. These supported catalysts combined with MAO were found to have high activity for the (co)polymerization of ethylene, propylene, and ethylene/l-octene, though the reaction products typically displayed broad molecular weight distributions. ... 

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