Hafnocene-based olefin polymerizations

Zirconocenes have been used for a long time in the field of olefin polymerization using MAO as cocatalyst. The equivalent hafnocenes were seldom used due to a lack of productivity while using MAO activation. In the last few years borane and borate activation has come into the focus of research for olefin polymerization. A variety of different hafnocenes were used to investigate the polymerization mechanism and the different cocatalysts. Differences in the polymer microstructures prepared with MAO and borate as cocatalysts are especially noted. While using TIBA/borate for building the active species, activities increase dramatically. Activities exceeded those of comparable Zr/MAO systems, obtaining high and ultrahigh molecular weight polypropylenes with molecular weights of up to 5,000,000 g mol^-1 and tacticities of 10-80% depending on the structure of the catalyst. 2009 Springer-Verlag Berlin Heidelberg.