No abstract

Metallocenes and other transition metal complexes, activated by methylaluminoxane allow the synthesis of polyolefins with a highly defined microstructure, tacticity, and stereoregularity. New copolymers, long chain branched polymers, and polyolefin nanocomposites are produced by these highly active catalysts. A better understanding of the structure of active sites for the olefin polymerization will lead to findings of new and simpler co-catalysts. Ethene or propene can be copolymerized with 1-olefin macromers with chain lengths up to 12,000 g mol(-1) as well as with cyclic olefins. Polypropenes of high molecular weight and filled with multi-walled carbon nanotubes show exciting new physical and mechanical properties and are prepared by in situ polymerization. These, and other polyolefin specialities, will be new future materials in a wide range of applications.

This paper shows the capability and advantage of the in-situ polymerization of olefins as a technique for the preparation of nanocomposites. The nanocomposites base on high molecular weight and highly isotactic polypropylenes and oxidized multi-walled carbon nanotubes (HMWiPP/MWCNT). Since a good interfacial adhesion between the matrix and the filler is crucial for the successful preparation of nanocomposites the polymerizations were performed with MAO anchored covalently to the surface of the nanotubes. Thus, a heterogeneous co-catalyst is formed and the polymerization starts directly on the tube surface. The resulting nanocomposites contain 0.9-25 wt% multi-walled carbon nanotubes and polypropylene with a molecular weight of about 1.4 9 10 6 g/mol. They were investigated with respect to their properties, like crystallization and melting temperature, as well as half-time of crystallization which decreases very strong in dependence on a rising filler content. The morphology analysis shows a homogeneous CNT distribution, a good separation of the individual particles, a very good interfacial adhesion and that every nanotube is covered by a thin polymer layer.