'Dual-side' catalysts for high and ultrahigh molecular weight homopolypropylene elastomers and plastomers

摘要

Classical Ziegler-Natta catalysts are capable of producing homopolypropylenes with high isotacticities. New trends are focussed on obtaining polypropy lenes with different properties through control of the polymer microstructure. Metallocene catalysts with variable structures revealed a great potential toward this challenge. The flexibility of the indenyl ligand substitution proved to be the key in controlling the stereoerror formation. Error type and error distribution have major implications on the mean isotactic sequence length, and therefore also on the mechanical properties of the polymer products. This review focuses on the synthesis of asymmetric ansa-metallocene catalysts, their polymerization mechanism and chain transfer reactions. 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.