Ethylene polymerization reactions with Ziegler–Natta catalysts. II. Ethylene polymerization reactions in the presence of deuterium

✍ Scribed by Y. V. Kissin; A. J. Brandolini

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 151 KB
• Volume: 37
• Category: Article
• ISSN: 0887-624X
• DOI: 10.1002/(sici)1099-0518(19991201)37:23<4273::aid-pola3>3.0.co;2-a

✦ Synopsis

Ethylene polymerization reactions with many Ziegler-Natta catalysts exhibit several features which differentiate them from polymerization reactions of ␣-olefins: a relatively low ethylene reactivity, higher polymerization rates in the presence of ␣-olefins, a high reaction order with respect to ethylene concentration, and strong reversible rate depression in the presence of hydrogen. A detailed kinetic analysis of ethylene polymerization reactions (see ref. 1) provided the basis for a new reaction scheme which explains all these features by postulating the equilibrium formation of a TiOC 2 H 5 species with the H atom in the methyl group ␤-agostically coordinated to the Ti atom in an active center. This mechanism predicts that the ␤-agostically stabilized TiOC 2 H 5 groups can decompose in the ␤-hydride elimination reaction with expulsion of ethylene and the formation of a TiOH bond even in the absence of hydrogen in the reaction medium. If D 2 is used as a chain transfer agent instead of H 2 , the mechanism predicts the formation of deuterated ethylene molecules, which copolymerize with protioethylene. To prove this prediction, several ethylene homopolymerization reactions were carried out with a supported Ziegler-Natta titanium-based catalyst in the presence of large amounts of D 2 . Analysis of gaseous reaction products and polymers confirmed the formation of several types of deuterated ethylene molecules and protio/ deuterioethylene copolymers, respectively. In contrast, a metallocene catalyst, Cp 2 ZrCl 2 OMAO, does not exhibit these kinetic features. In the presence of deuterium, it produces only DCH 2 OCH 2 O(CH 2 OCH 2 ) x OCH 2 OCH 2 D molecules.