Effect of Internal Lewis Base on Active Site Distribution for Ethylene/1-Octene Copolymerization by TiCl4/Lewis Base/ MgCl2 Catalysts

摘要

The molecular weight (MW) and polydispersity (PD) of polyethylene (PE) are important factors in determining the physical, mechanical, and rheological properties of polymers. While MW controls the mechanical properties of polymers, MWD mainly affects the rheological properties. Therefore, it is necessary to control the MW and PD to optimize the mechanical property and processibility of PE. One approach to control them is to physically blend polymers with different MW, and this technique is being widely applied in most industrial productions. Another method is to use a mixture of Ziegler-Natta/metallocene, or two metallocene catalysts, as well as a combination with different alkylaluminum cocatalysts. The conventional Ziegler-Natta catalyst and metallocene catalyst act as individual active species and thus produce a blend of PE with different MW. Dual-site catalysts can be further fine-tuned by changing polymerization such as temperature, pressure, hydrogen concentration, and comonomer content. Through the combination of different reactors and modification of operational conditions, the desired products are obtained, requiring significant investments.