Ethylene zirconocene catalysts

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. 

In order to estimate the quantity of catalyst which is required to produce a given amount of polyethylene, the productivity can be considered. The productivity of the high-pressure polymerization of ethylene with a zirconocene catalysts is in the range of 400 - 6,000 kg PE/g Zr. It depends steeply on the ratio of co-catalyst to catalyst, as well as on pressure and temperature. 

PP-b-PMMA (Mn = 22220, Mw/Mn = 1.14) was produced by CRP via another route. Terminally vinyl PP (Mn = 3100, Mw/Mn = 1.45, isotactic-ity = 32%) prepared using a zirconocene catalyst was converted to terminally brominated PP via PP-SiH prepared by hydrosilylation [70]. The resulting PP-b-PMMA was purified by extraction of unreacted PP with diethyl ether. Poly(ethylene-co-butene)-bZocfc-poly(methyl methacrylate) (EBR-b-PMMA) was synthesized through the bromination of terminally hydroxy-lated EBR (Mw = 3600 g/mol, Mw/Mn = 1.05), which was commercially available [71]. An atactic PP/PMMA had been synthesized by a combination of metallocene catalyses, Cp2ZrCl2 and Me2Si(CpMe4)(.W-f-Bu)TiCl2, and ATRP [72]. 

These were the first well-defined zirconocene catalysts capable of polymerising ethylene, propylene and higher a-olefins at high rates without the addition of any further activator. Metallocene catalysts obtained by abstraction of the Me-anion from Cp 2ZrMc2 by a strong Lewis acid, B(C6F5)3, were likewise found to exhibit high activity in ethylene and a-olefin polymerisation [30,105] ... 

Michelotti, M., Altomare, A. and Ciardelli, F., Ethylene/a-Olefins Cooligomerization versus Copolymerization by Zirconocene Catalysts , Polymer, 37, 5011-5016 (1996). 

Random copolymers of butadiene, isoprene and/or pentadiene with ethylene and/or propylene have been obtained in the presence of various catalysts, mainly based on Ti or V compounds [206,207]. Statistical butadiene/ethylene copolymers can also be formed with zirconocene catalysts [162]. 

Leclerc and Waymouth (119) and, independently, Arndt et al. (120) synthesized alternating copolymers of ethylene and propylene with zirconocene catalysts. The ethylene/propylene (EP) copolymerizations were carried out at 30 and 60°C for each of four metallocene catalysts (Me2C(3-RCp)(Flu)) ZrCl2 (R = H, Me, lsoPr, tertBu) (Fig. 10). As the size of the substituent increased, there were distinct changes in the copolymerization behavior and in the polymer microstructure. 

As an alternative approach, polycarbosilanes 42 bearing pendant zirconocene moieties have also been prepared by the ROP of the spirocyclic monomer 41 (Equation (14)). In this case, the materials were structurally characterized but the soluble fraction was of low molecular weight M < ca. 3,000) and the high molecular weight fraction was insoluble in organic solvents. In the presence of activators, both fractions functioned as ethylene polymerization catalysts with moderate activity. 

Metallocene catalysts were commercialized in 1991 by Exxon Chemical for the industrial production of ethylene-propylene (EP) elastomers in solution polymerization using zirconocene catalysts [37], As a result of extensive research of different metallocenes applied to the stereoregular control of polymeric materials, these systems were able to produce novel polymers such as syndiotactic polystyrene and ethylene-styrene copolymers, which were not possible to produce with traditional Ziegler-Natta catalysts. 

Liu, C., Tang, T., Zhao, Z., and Huang, B. 2002. Preparation of functionalized montmorillonites and their application in supported zirconocene catalysts for ethylene polymerization. Journal of Polymer Science, Part A Polymer Chemistry 40 1892-1898. 

Liu, C.-B., Tang, T., and Huang, B.-T. 2004. Zirconocene catalyst well spaced inside modified montmorillonite for ethylene polymerization Role of pretreatment and modification of mont-morillonite in tailoring polymer properties. Journal of Catalysis 221 162-169. 

A series of C symmetric ansa-zirconocene catalysts based on an ethylene bridged mixed ligand (indenylKfluorenyl) framework has been described (89). These complexes, upon activation with MAO, retain their high activities even at elevated polymerization temperatures producing PPs of variable isotacticities [mmmm] = 19.9-72.1% and molecular weights (Afw) up to 230,000 depending on... 

Thomas, E. J. Chien, J. C. W. Rausch, M. D. Influence of alkyl substituents on the polymerization behavior of asymmetric ethylene-bridged zirconocene catalysts. Organometallics 1999, 18, 1439-1443. 

Polyakov, O. G Rappe, A. K. Alternating ethylene/propylene copolymerization RFF molecnlar mechanics force field prognosticates effective zirconocene catalysts. Book of Abstracts, 218th National Meeting of the American Chemical Society, New Orleans, LA, Aug 22-26,1999 American Chemical Society Washington, DC, 1999 INOR-153. Chem. Abstr. 1999,1999, 541786. 

Ohva, L. Caporaso, L. Pellecchia, C. ZambeUi, A. Regiospecificity of ethylene-styrene copolymerization with a homogeneous zirconocene catalyst. Macrvmolecules 1995, 28, 4665-4667. 

Kaminsky, W. Spiehl, R. Copolymerization of cycloalkenes with ethylene in presence of chiral zirconocene catalysts. Makromol. Chem. 1989,190, 515-526. 

Naga, N. Imanishi, Y. Copolymeiization of ethylene and cyclopentene with zirconocene catalysts Effect of ligand structure of zirconocenes. Macromol. Chem. Phys. 2002, 203,159-165. 

The first success in this approach was norbomene-efliylene copolymerization in the presence of zirconocene catalysts [5]. Later, this method was refined and commercialized by researchers of Hoechst AG [6]. At present, norbomene-ethylene copolymers are manufactured by Ticona GmbH, (trademark Topas)... 

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