Copolymer Structure and Performance Consequences of High-Impact Ethylene-Propylene Copolymers Based on a Ziegler-Natta Catalyst with Novel Internal Donor

Catalyst development for advanced isotactic polypropylene copolymer grades cannot be considered without parallel work on the polymerization process, especially when multi-phase high-impact ethylene-propylene copolymers (also called heterophasic copolymers, HECOs) of complex composition are considered. Using a Ziegler-Natta type catalyst produced in an emulsion process and using citraconate ester as internal donor, a series of such high-impact copolymers is first produced in a bench-scale reactor. At this stage, the content of ethylene-propylene copolymer (EPC) phase is varied in a wide range for understanding the catalyst performance as well as the resulting structure-property relations, using three-stage polymerization to emulate multiple reactors. Selected compositions are subsequently scaled up to a multi-reactor pilot plant, demonstrating composition effects on mechanical performance. Both stages are accompanied by structural investigations using(13)C-NMR spectroscopy and atomic force microscopy. The novel catalyst is found to be capable of synthesizing HECOs in a wide range of elastomer (EPC) content, achieving free-flowing polymer powders up to an elastomer content as expressed by the xylene cold soluble fraction of 37 wt%.