Branched Polyethylene by Ethylene Homopolymerization withmeso-Zirconocene Catalyst

The polyethylene obtained in the presence of the catalyst constituted by the meso isomer of the prototypical zirconocene complex (ethylene)bis(1-indenyl)zirconium dichloride activated by methylalumoxane is characterized by the presence of ethyl branches. The intensities of the 13 C NMR signals associated with these branches indicate that there are about 1−2 ethyl groups per 100 monomer units. As a consequence, the melting temperature is 10−15 °C lower than the linear polyethylene obtained with the rac mixture of the same zirconocene complex. On the basis of kinetic evidence, a branching mechanism that involves a β-H transfer to the coordinated ethylene is proposed.