Stereospecific ethylene-styrene block copolymerization with ansa-zirconocene-based catalyst

rac-[Methylene(3-tert-butyl-1-indenyl)(2)]ZrCl2 activated by MAC, employed as catalyst in the ethylene-styrene copolymerization, shows a peculiar behavior. Actually, it produces block copolymers, whereas the homogeneous catalytic systems known to copolymerize these monomers preferentially give rise to alternating sequences of ethylene and styrene. The polystyrene blocks are isotactic and show crystallinity, also when their average length is as short as 10 units. Some evidence suggests the primary styrene insertion into the metal-carbon bond of the growing chain: this unusual regiochemistry could account for the observed tendency to give homosequences.