Production of polyolefins with controlled long chain branching and molecular weight distributions using mixed metallocene catalysts

摘要

Polyethylene with long-chain branches can be produced with certain metallocene catalysts, such as monocyclopentadienyl derivatives, by incorporation of macromonomers formed in-situ into the polymer backbone. This investigation demonstrates how dual metallocene systems can be used to control and enhance the level of long chain branching of polyethylene made with these catalysts. For instance, a catalyst that favors long chain branch formation, such as Dow's constrained geometry catalyst, can be combined with another metallocene that produces macromonomers at a faster rate. In this way, the concentration of macromonomers in the reactor increases, thus favoring the formation of long chain branches. This leads, however, to a complex microstructural control problem, since both the molecular weight and long chain branch distribution are affected simultaneously by the presence of the second catalyst. Several mathematical models will be used to describe this challenging microstructural. control problem. [References: 23]