Relationship between the Stereospecificity of Lanthanide Catalysts and the Structures of Active Sites and Dienes, the Nature of a Cocatalyst, and Preparation Conditions.

Autor: Monakov, Yu., Sabirov, Z., Urazbaev, V., Efimov, V.
Zdroj: Kinetics & Catalysis; May2001, Vol. 42 Issue 3, p310-316, 7p
Abstrakt: Several types of active sites can be formed during the polymerization of dienes in the presence of lanthanide catalytic systems. These sites differ in the nearest environment of a lanthanide atom (the numbers of chlorine and carbon atoms) and in the number of lanthanide–carbon bonds involved in chain growth. Quantum-chemical calculation shows that the π-allyl binding of the terminal unit of a growing polymeric chain with the lanthanide atom of an active site may be the reason for the cis-stereospecificity of the site. Therefore, the active sites containing electron-acceptor chlorine atoms that favor π-allyl binding can form cis-polydienes. Depending on the conditions of catalytic system preparation, primarily on the nature of an organic compound of a nontransition metal, one or another set of active sites is formed that can affect its stereospecificity. The quantitative analysis of kinetic data for diene polymerization shows that the anti-synisomerization of terminal units of growing polymeric chains made a certain contribution to the formation of trans-1,4 units in the presence of cis-regulating active sites. [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index
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