Syndiospecific polymerization of styrene by half-metallocene with a naphthoxy group ligand

A series of half-metallocenes of the type Cp’TiCl 2 (L) [Cp’ = Cp, L = naphthalen-1-yloxy ( 1a ), (2,4-dichloronaphthalen-1-yl)oxy ( 1b ), naphthalen-2-yloxy ( 1c ); Cp’ = C 5 Me 5 (Cp*), L = naphthalen-1-yloxy ( 2a )] are synthesized and well characterized. Using these complexes as catalysts for the polymerization of styrene in the presence of methylaluminoxane (MAO) cocatalyst, highly syndiotactic polystyrene can be obtained. The effects of anionic ligands, cyclopentadienyl, and polymerization conditions, such as Al/Ti molar ratio and polymerization temperature, on both the catalytic activity and the molecular weights of the resulted polymer are discussed. Higher polymerization temperature gives higher activity, but the obtained polymer has lower molecular weight. The higher Al/Ti ratio gives higher activity, while the molecular weight of the polymer increases with the increase of MAO amount in a certain range. This may indicate that the transfer to aluminum is not the main chain transfer mode of this polymerization. The activity of Cp* catalyst is higher than that of Cp catalyst, which indicates that the substituted methyls provides the stability of active center. Moreover, the molecular weight of the polymer obtained by the former is significantly higher than that of the latter, which indicates that the chain transfer reaction is inhibited by methyls on Cp ligand. Naphthyloxy ligands with different structures have no significant difference in polymerization activity and molecular weight of polymers.