Ziegler-type catalysts are both hierarchically complex and highly sensitive towards polar compounds, such as O 2 and H 2O, that complicate catalyst structure, polymerization activity and polymer properties studies 4, 5. In the case of propylene polymerization, additional Lewis base molecules are added either during the synthesis, which are called internal donors, or the polymerization reaction, which are called external donors, to provide local stereoregular control for the production of highly isotactic polypropylene 3. The current generation Ziegler-type catalysts are based on the chemisorption of a TiCl 4 pre-active site species on an activated MgCl 2 support matrix, followed by the reduction and alkylation with a trialkylaluminium co-catalyst 2.
The Ziegler-type (e.g., Ziegler and Ziegler-Natta) catalysts discovered in the 1950’s by Karl Ziegler and Giulio Natta are the dominant α-olefin polymerization catalysts for the production of different polyethylene grades, such as high-density polyethylene (HDPE) and isotactic polypropylene (i-PP) 1.
The combination of the spherical cap model system and the used advanced micro-spectroscopy toolbox, opens the route for high-throughput screening of catalyst functions with industrially relevant morphologies on the nano-scale. As a function of polymerization time, the fragmentation behaviour of the LaOCl framework changed from a mixture of the shrinking core (i.e., peeling off small polyethylene fragments at the surface) and continuous bisection (i.e., internal cleavage of the framework) into dominantly a continuous bisection model, which is linked to the evolution of the estimated polyethylene volume and the fraction of crystalline polyethylene formed. More specifically, a moisture-stable LaOCl framework with enhanced imaging contrast has been designed to support the TiCl 4 pre-active site, which could mimic the behaviour of the highly hygroscopic and industrially used MgCl 2 framework. Here, the missing link in the morphology gap between planar model systems and industrially relevant spherical catalyst particles is introduced through the use of a spherical cap Ziegler-type catalyst model system for the polymerization of ethylene. Polyolefin catalysts are characterized by their hierarchically complex nature, which complicates studies on the interplay between the catalyst and formed polymer phases.
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