Advances in Ziegler-Natta catalysts for polypropylene

摘要

The most advanced catalysts, based on MgCl2-supported TiCl4 and electron donors, are able to provide polypropylenes with an isotacticity higher than 99%. This, together with the continuous progress made in understanding and exploiting the role of electron donors in controlling polymer MW and MWD, has led to polypropylene products having an unprecedented level of stiffness or stiffness/impact balance. On the other hand, other potential fields of application exist where rigidity is not required and, actually, the key property is softness rather than stiffness. As a matter of fact, it has clearly been established that soft polypropylenes can be more attractive from the business standpoint than their stiff counterparts. Generally, these materials are multiphase copolymers obtained via sequential gas-phase copolymerization of propylene and ethylene-propylene mixtures using the morphology-control led conventional MoCl2-TiCl4 catalysts based on the couple phthalate-silane as internal and external donors. This communication deals with a new class of donors that can be used either as external donors in combination with phthalates (A) or as internal/external donors (B).