Unbridged zirconium and titanium metallocenes with seven- or eight-saturated fused-ring ligands: a route for the synthesis of stereoblock polypropene

Unbridged zirconocene catalysts, where a seven- or eight-membered ring fused to a cyclopentadiene is associated with a phenyl substituent in position 2(C7Ph-Zr and C8Ph-Zr), were tested, under the same polymerization conditions, to produce polypropenes with micro structure, molecular properties, and thermal behavior similar to those prepared with (IndPh)(2)ZrCl2 (W-Zr), the "classical" Waymouth catalyst. Different results were obtained from the homologue titanium catalysts (C7Ph-Ti and C8Ph-Ti) and from the titanium benzyl derivative (C7Bn-Ti), which produced quite heterogeneous materials with broad molecular weight and that can be separated into fractions spanning from completely atactic to fractions characterized by the presence of long isotactic blocks. A quite interesting behavior is observed with the zirconium benzyl derivative C7Bn-Zr, which produces good yields of a polymer with narrow polydispersity, which, despite its rather high isotacticity, shows a hardly detectable melting peak and is completely ether soluble. Quite surprisingly, the same sample, after prolonged annealing, shows a narrow melting peak at low temperature (55-65 degrees C). This result, together with the X-ray analysis, is in favor of a quite homogeneous material, capable of giving crystallites of small size.