Branched polyethylene by ethylene homopolymerization with meso-zirconocene catalyst

The polyethylene obtained in the presence of the catalyst constituted by the meso isomer of the prototypical zirconocene complex (ethylene)bis(l-indenyDzirconium dichloride activated by methylalumoxane is characterized by the presence of ethyl branches. The intensities of the 13C 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 9-H transfer to the coordinated ethylene is proposed. © 1999 American Chemical Society.