SUPPORTED BIS(INDENYL)-CHROMIUM AND BIS(FLUORENYL)-CHROMIUM CATALYSTS FOR ETHYLENE POLYMERIZATION

Experimental data are presented which demonstrate that silica-supported bis(indenyl)- and bis(fluorenyl)-chromium catalysts have good activity in ethylene polymerization. For maximum productivity with the indenyl chromium catalyst, the silica must be dried, with higher dehydration temperatures giving a significant increase in polymerization activity. In contrast to the behavior of supported chromocene catalysts, the indenyl- and fluorenyl-chromium catalysts require a higher hydrogen/ethylene ratio to achieve a specific polymer melt index. Nevertheless, highly saturated polyethylenes are produced with these new catalysts. This result indicates that chain transfer to hydrogen remains the major chain transfer reaction. The overall results are consistent with an active-site model which comprises a supported divalent chromium center attached to an indenyl or fluorenyl ligand during the polymerization process.