Sequence and Stereoselectivity of the <i>C</i>₁-Symmetric Metallocene Me₂Si(1-(4,7-Me₂Ind))(9-Flu)ZrCl₂

Abstract

The homo- and copolymerization behaviors of two C1-symmetric metallocenes Me2Si(Ind)(9-Flu)ZrCl2 (2) and Me2Si(1-(4,7-Me2Ind))(9-Flu)ZrCl2 (3) in the presence of methylaluminoxane (MAO) are compared. In liquid propylene at 0 °C, metallocene 2 yields a predominantly isotactic polypropylene of low tacticity ([mmmm] = 27%) where metallocene 3 produces syndiotactic polypropylene (74% [rrrr]). The stereoselectivity of metallocene 3 depends on monomer concentration: the percentage of syndiotactic pentads [rrrr] in polymers derived from 3 increases with increasing monomer concentration. Copolymerization of ethylene and propylene with metallocenes 2 and 3 yields highly alternating but atactic ethylene−propylene copolymers.