Martin Antberg’s research while affiliated with Hospital Frankfurt Hoechst and other places

Chiral bridged bisindenyl zirconoeenes with special substitution patterns on the aromatic rings are potentially commercial catalysts for the production of isotactic polypropylenes. The performance characteristics of these systems are different, the variations being induced by size and position of the substituents. The novel catalysts will be used for the production of new iPP grades with enhanced properties or unprecedented property combinations. Typical features of metailocene iPP polymers are higher stiffness, higher transparency, and a lower level of extractables than conventional products. The most recent new designs of metailocene PP catalysts are discussed. These include asymmetric systems and metallocenes inducing two-step-polymerization mechanisms.

The synthesis of seven new bridged zirconocenes is described, which make isotactic polypropylene when used in polymerizations of propylene with methylaluminoxane as cocatalyst. Their polymerization behavior in propylene and ethylene polymerizations is examined and discussed. Aromatic substituents in appropriate positions of the zirconocene ligand frame result in catalysts with activities, stereospecificities, and polypropylene molecular weights much higher than those of any previously described metallocene system. By structure variations it is demonstrated that the effectiveness of these substitutions strongly depends on their position and on a nonincremental synergism with alkyl substituents on the ligand frame. The high activities of the systems can be explained well by electronic effects, whereas steric effects obviously play the more important role for the high stereospecificities and high molecular weights of the polymers.

A breakthrough for the technical application of zirconium catalysts in isotactic propylene polymerization has been achieved with complexes 1. The highest molecular mass of polypropylene, the best isotacticity, and the highest activity of all catalysts are provided by 1, R1 = R3 = CH3, R2 = i-C3H7. Hydrogenation of the six-membered ring drastically lowers the activity and the molecular mass obtained.

Polypropylene having isotacticities 94-98% and mol. wt. (32-46) × 103 was prepd. using I (R1 = H, Me, Et; R2 = H, Pr-iso; R3 = Me,Ph) or II (R1 = H, Me, Et) in combination with methylaluminoxanes as catalysts. [on SciFinder(R)]

Polypropylene homopolymers made by three different stereorigid metallocene catalysts (two isospecific, one syndiospecific) are compared with each other and with commercial samples made by a heterogeneous catalyst. The comparison includes mechanical properties, DSC-, 13-C NMR- and WAXS-data. The correlation between microscopic data and macroscopic properties is discussed. A novel particle-forming process in propylene bulk polymerization with stereorigid metallocene catalysts is demonstrated and discussed.