Metallocene-catalyzed ethene polymerization : long-chain branched polyethene

Kokko, Esa

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Metallocene-catalyzed ethene polymerization : long-chain branched polyethene



Title:	Metallocene-catalyzed ethene polymerization : long-chain branched polyethene
Author(s):	Kokko, Esa
Date:	2002-09-06
Language:	en
Pages:	52, [98]
Department:	Department of Chemical Technology Kemian tekniikan osasto
ISBN:	951-22-6080-8
Series:	Acta polytechnica Scandinavica. Ch, Chemical technology series, 290
ISSN:	1239-0518
Subject:	Chemistry
Keywords:	metallocene catalysts, polyethylene, copolymerization, characterization, long-chain branching, rheology
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Abstract: Long-chain branches and narrow molecular weight distribution is a novel structure combination in polyethene, which has only been possible to achieve with single-center catalysis. Long-chain branches, even at very low concentrations, have a strong effect on the polymer melt behavior and, thereby, the processing properties. This work deals with ethene polymerization using group IV metallocene catalysts and the examination of long-chain branching in polyethene. Long-chain branching in metallocene catalysis is believed to take place via a copolymerization route, in which a vinyl terminated polyethene chain is incorporated into a growing polymer chain. Understanding the chain transfer mechanisms (vinyl end-group formation) and copolymerization abilities of metallocene catalysts have been important issues in this work. The examination of the polymerization behavior of several metallocene compounds revealed that chain transfer mechanisms were catalyst specific. Depending on the catalyst structure, the termination of chain growth occurred via β-H elimination, chain transfer to the monomer, or chain transfer to the cocatalyst. The vinyl selectivities were between 20 and 100%. Comonomer response in ethene and 1-olefin copolymerization also depended on the catalyst structure. 10-fold differences in comonomer reactivity ratios were observed. Long-chain branching analysis of homopolyethenes produced with different metallocene catalysts indicated that the catalysts with high vinyl selectivity and good copolymerization ability were the most prominent in producing a polymer with modified rheological properties. In addition to rheological measurements, 13C NMR spectroscopy also showed the presence of long-chain branches. Besides the choice of catalyst, the polymerization conditions had a major impact on long-chain branch contents. Adjusting the ethene, hydrogen, or comonomer (1-olefin or nonconjugated α,ω-diene) concentration changed the rheological properties of the polymers.
Parts: Malmberg, A., Kokko, E., Lehmus, P., Löfgren, B., Seppälä, J.V., Long-Chain Branched Polyethene Polymerized by Metallocene Catalysts Et[Ind]<sub>2</sub>ZrCl<sub>2</sub>/MAO and Et[IndH4]<sub>2</sub>ZrCl<sub>2</sub>/MAO, Macromolecules 31 (1998) 8448-8454. Lehmus, P., Kokko, E., Härkki, O., Leino, R., Luttikhedde, H.J.G., Näsman, J.H., Seppälä, J.V., Homo- and Copolymerization of Ethylene and alpha-Olefins over 1- and 2-Siloxy-Substituted Ethylenebis(indenyl)zirconium and Ethylenebis(tetrahydroindenyl)-zirconium Dichlorides, Macromolecules 32 (1999) 3547-3552. Kokko, E., Malmberg, A., Lehmus, P., Löfgren, B., Seppälä, J. Influence of the Catalyst and Polymerization Conditions on the Long-Chain Branching of Metallocene-Catalyzed Polyethenes, J. Polym. Sci. Part A: Polym. Chem. 38 (2000) 376-388. Kokko, E., Lehmus, P., Leino, R., Luttikhedde, H.J.G., Ekholm, P., Näsman, J.H., Seppälä, J.V., meso- and rac-Diastereomers of 1- and 2-tert-Butyldimethylsiloxy Substituted Ethylenebis(indenyl)zirconium Dichlorides for Formation of Short- and Long-Chain Branched Polyethene, Macromolecules 33 (2000) 9200-9204. Kokko, E., Lehmus, P., Malmberg, A., Löfgren, B., Seppälä, J., Long-Chain Branched Polyethene via Metallocene-Catalysis: Comparison of Catalysts. In Organometallic Catalyst and Olefin Polymerization, Catalysts for a New Millennium, Blom, R., Follestad, A., Rytter, E., Tilset, M., Ystenes, M (Eds.) Springer, 2001, 335-345. Kokko, E., Pietikäinen, P., Koivunen, J., Seppälä, J.V., Long-Chain-Branched Polyethene by the Copolymerization of Ethene and Nonconjugated α,ω-Dienes. J. Polym. Sci. Part A: Polym. Chem. 39 (2001) 3805-3817. Kokko, E., Wang, W.-J., Zhu, S., Seppälä, J.V., Structural Analysis of Polyethene Prepared with rac-Dimethylsilylbis(indenyl)zirconium Dichloride/Methylaluminoxane in High-Temperature Continuous Stirred-Tank Reactor, J. Polym. Sci. Part A: Polym. Chem. 40 (2002) 3292-3301. Gabriel, C., Kokko, E., Löfgren, B., Seppälä, J.V., Münstedt, H., Analytical and Rheological Characterization of Long-Chain Branched Metallocene-Catalyzed Ethylene-Homopolymers, Polymer 43 (2002), in press.
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