Alternating ethylene-styrene copolymerization with a methylaluminoxane-free half-titanocene catalyst

Copolymerization of ethylene and styrene in the presence of the catalytic system eta(5)-C(5)Me(5)-Ti(CH(2)Ph)(3)-B(C6F5)(3) has been investigated. Independently from the feed composition, basically alternating ethylene-styrene copolymers are obtained, together with some polyethylene and syndiotactic polystyrene, from which the former can be separated by solvent extraction. NMR analysis of suitably C-13-enriched end groups shows that the regiospecificity of styrene insertion in the initiation step is largely secondary. A tentative explanation for the preferentially alternating comonomer incorporation is proposed