E Stereoregular 1,1 and 1,3 Constitutional Units from 1,3-Butadiene in Copolymerizations Catalyzed by a Highly Hindered C2 Symmetric Metallocene
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- 作者：Pasquale Longo ; Stefania Pragliola ; Giuseppe Milano ; and Gaetano Guerra
- 刊名：Journal of the American Chemical Society
- 出版年：2003
- 出版时间：April 23, 2003
- 年：2003
- 卷：125
- 期：16
- 页码：4799 - 4803
- 全文大小：103K
- 年卷期：v.125,no.16(April 23, 2003)
- ISSN：1520-5126
文摘
Unprecedented 1,1 and 1,3 constitutional units from 1,3-butadiene, both presenting only the Econfiguration of the double bond, have been achieved by copolymerization with ethene, conducted at hightemperature and low ethene concentration, when catalyzed by a highly hindered C2 symmetric metallocene.Ethene/butadiene copolymerizations by this catalyst generally lead to prevailing methylene-1,2-cyclopropaneunits from butadiene. Polymer microstructures obtained for different comonomer concentrations clearlyindicate that the rate-determining step leading to cyclopropanation involves ethene, while that leading to1,1 and 1,3 constitutional units does not. A general copolymerization scheme and a molecular modelingstudy of the cyclopropanation reaction are presented. Molecular modeling also indicates that the Estereoselectivity for 1,1 and 1,3 constitutional units can be rationalized, in the assumption that an allylisomerization of the terminal of the growing chain would occur.