Amorphous Polypropylene by Half-Titanocene Catalysts with Improved Elastomeric Properties

Nonbridged half-titanocenes containing anionic donor ligands of type, Cp'=TiX2(Y) (Cp'= cyclopentadienyl group and Y = aryloxo, ketimide, phosphinimide, etc.), are reported to be active for syntheses of new ethylene copolymers. The aryloxo or the ketimide analogues, are efficient for the copolymerization of ethylene with sterically encumbered olefins or cyclic olefins. However, as far as we know, examples of homo and copolymerization of propylene with aryloxo or the ketimide modified analogues are not found in the literature. Thus, we herein report the synthesis of polypropylene using different ketimide modified half-titanocene catalysts (Cp'=TiCl2(N=CtBu) [Cp'= Cp (1), C5Me5 (2) and Me3SiC5H4 (3)], in the presence of MAO as cocatalyst, at different pressure and temperatures. The microstructures and molecular weights of the resultant homopolymers, and their thermal and mechanical properties were determined. The ketimide-modified Cp?TiCl2(N CtBu2) (1 and 3) exhibited higher catalytic activities and yielded higher molecular weight polypropylene up to 820 Kg/mol, that could be defined as ultrahigh molecular weight polypropylene. All the synthesized polypropylenes are atactic and highly regioregular, with predominant rrrr pentads, especially with catalyst 1. Differential scanning calorimetry (DSC) confirmed the identity of the polymers as wholly amorphous aPP, with no melting endotherm observed. Glass transitions were observed between -2 and 1 °C. These polypropylenes have been found to be high-performance thermoplastic elastomers exhibiting remarkably high ductility, with a tensile strain at break of >2000%.