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

Polyethylene with long-chain branches can be produced with certain metalloc ene catalysts, such as monocyclopentadienyl derivatives, by incorporation o f macromonomers formed in-situ into the polymer backbone. This investigatio n demonstrates how dual metallocene systems can be used to control and enha nce the level of long chain branching of polyethylene made with these catal ysts. For instance, a catalyst that favors long chain branch formation, suc h as Dow's constrained geometry catalyst, can be combined with another meta llocene that produces macromonomers at a faster rate. In this way, the conc entration of macromonomers in the reactor increases, thus favoring the form ation of long chain branches. This leads, however, to a complex microstruct ural control problem, since both the molecular weight and long chain branch distribution are affected simultaneously by the presence of the second cat alyst. Several mathematical models will be used to describe this challengin g microstructural. control problem.