The influence of substituents in metallocene on propylene polymerization

Two new unbridged zirconocenes, bis(2.4,7-trimethyl indenyl)zirconium dichl oride (Met-I) and bis(2-methyl-4,7-diethyl indenyl)zirconium dichloride (Me t-II) were prepared in order to investigate the steric effects of substitue nts on the nature of the catalysts for the: polymerization of propylene. A mixture of methyl aluminoxane (MAO) and triisobutylaluminum [Al(iBu)(3)] wa s used as cocatalyst to activate these catalysts. The decrease in steric bu lkiness of substituents at 4 and 7 positions of the indenyl ring resulted i n an increase of both activity and molecular weight as well as the isotacti city.