29. Highly Isospecific Heterogeneous Metallocene Catalysts Activated by Ordinary Alkylaluminums

Abstract

Abstract Tetrachlorosilane or 1,1,2,2-tetrabromoethane was reacted with the surface hydroxyl groups of silica gel and the resulting chemically modified silica gel was brought into contact with lithium salt of indene. The catalyst precursors thus prepared were then reacted with zirconium tetrachloride to obtain the immobilized heterogeneous metallocene catalysts. Polymerization of propene was conducted with them using either methylalumoxane or common trialkylaluminums as cocatalyst. Since the catalysts may contain a mixture of meso and racemic isomers which give atactic and isotactic polypropene, the polymer produced was fractionated by extracting with boiling heptane. It was found that the catalysts can be easily activated by ordinary trialkylaluminums to give highly isotactic polypropene with the melting point as high as over 162°C. Similar catalysts were also prepared using fluorene as ligand, which gave not syndiotactic but highly isotactic polypropene.