Polymerization of ethylene initiated with trisiloxane-bridged heterometallic dinuclear metallocene

Abstract

The new trisiloxane-bridged heterometallic dinuclear metallocenes, hexamethyltrisiloxanediyl (cyclopentadienyltitanium trichloride) (cyclopentadienylindenyl zirconium dichloride), Cl3Ti-CP(CH3)(2)Si-O-Si(CH3)(2)-O-Si(CH3)(2)-Cp-ZrIndCl(2) (CH3)(2)-Cp-ZrIndCl(2) (1) and hexamethyltrisiloxanediyl (cyclopentadienylindenylhafniun dichloride) (cyclopentadienylindenyl zirconium dichloride), Cl(2)IndHf-Cp(CH3)(2)Si-O-Si(CH3)(2)-O-Si(CH3)(2)Cp-ZrIndCl(2) (2) connecting two dissimilar metallocenes were synthesized and used for ethylene polymerization in the presence of modified methylaluminoxane (MMAO) cocatalyst. The catalytic activity of heterometallic dinuclear metallocenes, 1 and 2 was lower than that of corresponding mononuclear metallocene as well as two physically mixed catalysts, CpTiCl3/Cp2ZrCl2 and Cp2HfCl2/Cp2ZrCl2. On the other hand, MWD of PE obtained with 1 and 2 was remarkably broader (M-w/M-n became up to 9.4) than those of PEs prepared with the corresponding mononuclear metallocenes and mixed catalysts. With analysis by GPC and CFC, it was found that PE produced by the heterometallic dinuclear metallocenes exhibited the definite bimodal GPC curves that should cause the broadening of MWD