Asymmetric metallocene catalysts: design of ultrahigh molecular weight polypropylene plastomers
FacultiesFakultät für Naturwissenschaften
LicenseStandard (Fassung vom 03.05.2003)
This study focuses on the synthesis of novel asymmetric ansa-metallocene catalysts of the indenyl-fluorenyl type, designed to tailor the microstructures of the resulting polypropylenes so that the portfolio of the material properties is extended toward ultrahigh molecular weight plastomers. These materials offer both the flexibility of conventional elastomers and the processing properties of thermoplastics, plus various combinations of special features, such as good heat resistance and excellent optics. The newly designed catalysts are characterized by the upgraded substitution pattern and ligand design, necessary for the improvement of catalyst polymerization properties and microstructure of the resulting polymers. A detailed analysis of the influences that polymerization temperature and monomer concentration exhibit on polymer microstructure reveals a "back-skip" polymerization mechanism in analogy with similar C1-symmetric catalysts studied so far. Additionally, these catalysts lead to ultrahigh molecular weight materials with excellent elasticity and glass transition temperature and, especially, high content of incorporated ethylene when used in propylene/ethylene copolymerization experiments. A set of thermal and mechanical analyses (GPC, DSC, WAXS, DMA) correlated with NMR allow a detailed study of the polymer microstructures, morphologies and mechanical properties. Next, this knowledge is used in order to precisely explain the behavior of the polymeric materials, produced with different types of catalysts, in terms of isotactic block length and not of stereodefects. The impact of the presented asymmetric ansa-metallocene extends beyond simple propylene polymerization disclosing a way to materials that fill the gap between "soft" thermoplastic elastomers and stiff polypropylene materials.
Subject HeadingsMetallocene [GND]
Metallocene catalysts [LCSH]