On the sensitivity of metallocene catalysts toward molecular hydrogen during ethylene polymerization

Polymerization of ethylene has been performed with heterogenised metallocen e catalysts in the presence of hydrogen as chain transfer agent in a slurry semi-batch reactor. On-line GC analyses show that both Cp2ZrCl2/MAO/SiO2 a nd Cp-2*ZrCl2/MAO/SiO2 are much more reactive toward hydrogen as compared t o commercial catalysts such as CrO/SiO2 and CrCp2/SiO2. While narrow molecu lar weight distributions ate obtained for the polymer produced with the met allocene catalysts in the absence of hydrogen, broad distributions are obta ined when hydrogen is present. The broadening is at least partly a conseque nce of the way hydrogen is introduced, but especially for Cp-2*ZrCl2/MAO/Si O2, more than one active site might be present. Polymerizations with deuter ium show that both metallocene catalysts react cleanly with deuterium, form ing -CH2D fragments.