Process for obtaining polyolefins with broad bimodal or multimodal molecular weight distributions

Abstract

The process is characterized by the use of catalyst systems consisting of a single metallocene catalyst activated with mixtures of at least 2 co-catalysts. The co-catalysts are aluminium alkyls, aluminoxanes or boron compounds. Different active centers are produced in the catalyst through the use of these mixed co-catalyst systems, each having different rates of initiation and completion of the polymerization reaction, which give rise to polyolefins with different molecular weights, resulting in products with broad bimodal or multimodal molecular weight distributions and the incorporation of co-monomer can be controlled by appropriate selection of the metallocene and use of combinations of different types of co-catalysts, as well as by varying the reactor pressure, the reaction temperature and the molar ratios between the various components of the catalyst system. A broad bimodal or multimodal molecular weight distribution can be achieved in both the presence and absence of hydrogen during the polymerization reaction. Likewise broad bimodal and multimodal molecular weight distributions can be obtained in polymers by varying the order in which the components of the catalyst system are added. This process may also be used with both homogeneous and heterogenous metallocene catalysts.