Behavior of Metallocene Olefin Polymerization Catalysts under High Pressure

Since the discovery of homogeneous Ziegler-Natta catalysts, many efforts have been made in their practical application. Metallocene-catalyzed olefin polymerization under high pressure has recently attracted research interest since a high-pressure polymerization process has become a probable method for the industrial utilization of these catalysts. There have been some reports on high-pressure olefin polymerization using group 4 metallocene catalysts. However, the effects of pressure on various parameters, such as chain-transfer rates or the concentration of active species, have not been well described. We recently reported that metallocene-catalyzed olefin polymerization was remarkably accelerated by high pressures up to 1500 MPa. Herein we wish to describe the behavior of group 4 metallocene complex - methylalu-minoxane (MAO) catalyst systems under high pressure in terms of their termination processes in olefin polymerization. The effects of high pressure on some chain-transfer reactions and the concentration of active species are discussed.