Cp2ZrCl2/异丁基铝氧烷催化乙烯聚合动力学

均相茂金属催化烯烃聚合体系大多采用甲基铝氧烷(MAO)为助催化剂,但对MAO的作用机理尚不清楚。据文献报道,乙基铝氧烷(EAO)和异丁基铝氧烷(BAO)也有类似的助催化作用,但聚合活性远低于MAO体系。

A Kinetic Study on Ethylene Polymerization by Cp2ZrCl2/iso-Butylalumoxane

iso Butylalumoxane(BAO) has been synthesized and characterized, and ethylene polymerization catalyzed by Cp 2ZrCl 2/BAO has been investigated. The polymerization rate curves at different catalyst concentrations, Al/Zr molar ratio and polymerization temperature are determined and compared to the kinetic behavior of ethylene polymerization catalyzed by Cp 2ZrCl 2/methylalumoxane(MAO) reported in literature. On the basis a tentative model for the cocatalytic action of BAO has been proposed: only a kind of multi molecular aggregates of BAO can act as cocatalyst of metallocenes. Because of the low stability of the BAO aggregates, Cp 2ZrCl 2/BAO system shows a moderate catalytic activity only at relatively high BAO concentration and medium temperature. The main reason for the lower activity of BAO than MAO is the absence of highly active species which is stable at low concentration and high temperature.