Polymerization Behavior of C1-Symmetric Metallocenes (M = Zr, Hf): From Ultrahigh Molecular Weight Elastic Polypropylene to Useful Macromonomers

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• 作者：Alexander Sch枚bel ; Dominik Lanzinger ; Bernhard Rieger
• 刊名：Organometallics
• 出版年：2013
• 出版时间：January 28, 2013
• 年：2013
• 卷：32
• 期：2
• 页码：427-437
• 全文大小：494K
• 年卷期：v.32,no.2(January 28, 2013)
• ISSN：1520-6041

文摘

The C₁-symmetric metallocenes rac-[1-(9-畏⁵-fluorenyl)-2-(5,6-cyclopenta-2-methyl-1-畏⁵-indenyl)ethane]zirconium dichloride (1) and rac-[1-(9-畏⁵-fluorenyl)-2-(5,6-cyclopenta-2-methyl-1-畏⁵-indenyl)ethane]hafnium dichloride (2) are known to produce elastic polypropylene. They were investigated concerning their temperature stability during the polymerization of propene. After activation of these complexes with triisobutylaluminum (TIBA)/[CPh₃][B(C₆F₅)₄], first polymerization experiments (80鈥?00 掳C) afforded moderate to high activities. However, at these polymerization temperatures, the molecular weights of the produced polymers are significantly decreased, resulting in a waxy appearance and, therefore, a loss of the elastic behavior. The main reason for this behavior, especially for the more significant decrease of the molecular weight in the case of hafnocene 2 compared with zirconocene 1, was revealed to occur due to a fast 尾-methyl transfer reaction. Hence, hafnocene 2 can form polymer chains with a high selectivity toward allylic chain ends. These macromonomers can be used in the catalytic insertion polymerization for the formation of new grafted copolymers. Initial copolymerization experiments with ethene were conducted.