Core–Shell Particles DOI: 10.1002/anie.200902047 Spatially Resolved Catalysis for Controlling the Morphology of Polymer Particles** Till Diesing, Giovanni Rojas, Markus Klapper,* Gerhard Fink, and Klaus Müllen* Morphology control is essential when optimizing the proper- ties of polymer blends and inorganic–organic hybrid materi- als. [1, 2] Properties such as mechanical stability, impact strength, or scratch resistance are adjusted by the homoge- neous incorporation of a second polymer or inorganic particles into the blend. However, simple blending of two distinct materials can lead to ill-defined mixtures with an irregular component distribution. Block, graft, or other copolymers can be used as compatibilizers to overcome these drawbacks. [3, 4] Synthesis of these polymers, however, requires living polymerization techniques, and prediction of the resulting morphologies by employing theoretical models is difficult. In another approach, which is mainly used for dispersions that are applied as paints and coatings, core–shell particles that consist of two polymers are generated by emulsion polymerization. [5] Both processes are unsuitable for olefins and the sensitivity of the required catalysts means that aqueous emulsions are not applicable to olefin polymeri- zation. Compatibilization of polyolefins with different poly- mers is also a challenge because of the lack of compatibilizing block copolymers. [6–7] The problem of obtaining polyolefins with a core–shell morphology can be only partially solved by using a complex reaction sequence, [8] in which the polyolefin obtained after a first gas-phase polymerization is transferred into another reactor that contains the second monomer. [9] However, this process is both expensive and complicated, and needs to be adjusted for special polymer mixtures. The development of versatile methods for the generation of more complex polymer morphologies in particles, especially for polyolefins, remains a challenge. It is already known that supporting catalysts are required to adjust the morphology (such as size and bulk density) of polyolefin particles. [8] The control is mainly achieved by shape replication of the supporting particles in the product particle. The ability of a support to fragment into smaller particles during the polymerization process (Figure 1) is decisive for the replication process, which generally occurs in a stepwise fashion from the outer to the inner shell of the support (Figure 1). [10] We proposed the use of a replication effect to not only control the shape of the particles, but also to generate an inner morphology (core–shell structure) during polymerization. We thus anticipated that the loading of different catalysts in different layers of a spherical support would result in the spatially resolved formation of different polymer layers in a product particle. A nanostructured catalyst system can act as a template for the formation of the final morphology in the product particle (Figure 2). As both the immobilized catalysts and the polymers were expected to be migrationally stable under the reaction conditions, the final product should represent the structure of the initial catalytic system. To verify this concept, we studied the formation of a core– shell product particle that consists of different types of polypropylene (PP). We report herein a catalyst system in which two metallocene catalysts produce polypropylene with different tacticities. The two catalysts are spatially resolved in the different layers of an inorganic–organic hybrid particle with an inorganic core and an organic shell. The production of the well-defined core–shell catalyst particles is based on three synthetic steps: 1) formation of a Figure 1. Fragmentation process of a pure silica catalyst (the pure “core” of a core–shell catalyst). Figure 2. Olefin polymerization induced by a particle with two catalytic domains. Formation of two distinct polymers in one step under constant reaction conditions. [*] T. Diesing, Dr. G. Rojas, Dr. M. Klapper, Prof.Dr. K. Müllen Max Planck Institute for Polymer Research Ackermannweg 10, 55128 Mainz (Germany) Fax: (+ 49) 6131-379-100 http://www.mpip-mainz.mpg.de/ E-mail: klapper@mpip-mainz.mpg.de muellen@mpip-mainz.mpg.de Prof. Dr. G. Fink Max-Planck-Institut für Kohlenforschung Kaiser-Wilhelm-Platz 1, 45470 Mülheim an den Ruhr (Germany) [**] We are grateful to Dr. K. Koynov, G. Glasser, and Dr. M. Wagner for LSCFM, SEM, and 13 C NMR measurements. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.200902047. Communications 6472  2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2009, 48, 6472 –6475