Exploring pathways to reduce the distribution of active sites in the Ziegler–Natta polymerization of propylene |
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Authors: | David Ribour Valérie Bollack‐Benoit Vincent Monteil Roger Spitz |
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Affiliation: | 1. Chimie Catalyse Polymères Procédés (C2P2), UMR 5265, CNRS/CPE Lyon/UCBL, Equipe Chimie et Procédés de Polymérisation (LCPP), 43, bd du 11 Novembre 1918, Bat. 308F, BP 2077, 69616 Villeurbanne Cedex, France;2. Chimie Catalyse Polymères Procédés (C2P2), UMR 5265, CNRS/CPE Lyon/UCBL, Equipe Chimie et Procédés de Polymérisation (LCPP), 43, bd du 11 Novembre 1918, Bat. 308F, BP 2077, 69616 Villeurbanne Cedex, FranceChimie Catalyse Polymères Procédés (C2P2), UMR 5265, CNRS/CPE Lyon/UCBL, Equipe Chimie et Procédés de Polymérisation (LCPP), 43, bd du 11 Novembre 1918, Bat. 308F, BP 2077, 69616 Villeurbanne Cedex, France |
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Abstract: | Chemical treatments of classical supported Ziegler–Natta precatalysts were conducted by using additional bulky ligands to attempt to narrow and homogenize the active sites distribution in propylene polymerization. Additions of monodentate ligands such as bis(trimethylsilyl)amide, cyclopentadienyl derivates or triphenylsilanol were seen to slow down the polymerization without modifying the distribute properties of polypropylenes. In the case of multidentate ligands (porphines or biquinolines), in addition to the poisoning of active sites, an extraction of titanium from the catalyst surface is observed. A decrease of both melting point and isotacticity (II%) of polymers using these compounds suggest that the most isospecific titanium sites are first extracted from the MgCl2‐surface. The narrowing of the molecular weight distribution confirms that the highly isospecific sites are the most active sites, producing the higher molecular weight polymers. Moreover, this study shows that the distributed properties of polymers are due to the chemical diversity of the active sites with various steric and electronic environments at the catalyst surface and not to mass transfer limitations. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3941–3948, 2007 |
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Keywords: | active sites distribution isotactic MgCl2‐supported catalysts poly(propylene) Ziegler– Natta polymerization |
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