Syndiotactic-Atactic Stereoblock Polystyrene Obtained with a Hapto-Flexible Catalyst

Half-titanocene (CpCH2CH2OCH3)TiCl3 (1), (Cp = cyclopentadienyl), activated by methylaluminoxane (MAO), has been tested in the polymerization of styrene in a suitable range of temperatures, obtaining a new material consisting of syndiotactic-atactic stereoblocks of polystyrene. The monoanionic bidentate ancillary ligand of the titanium based catalyst, consisting of a cyclopentadienyl bearing an alkyl ether, is a hapto-flexible ligand because the ether group can either be coordinated or not to the metal, depending on reaction temperature. Thus, the ether group can give rise to two possible catalytic sites: (i) syndiospecific, when the ether group is not coordinated to the metal center, and (ii) aspecific, when it is coordinated to titanium. Consequently, it produces polymer chains having syndiotactic and atactic stereoblocks. In fact, in the range of temperature considered (0-19 degrees C), syndiotactic polystyrene was produced at 19 degrees C, atactic polystyrene at 0 and 5 degrees C, and syndiotactic-atactic stereoblock polystyrene at 10 and 15 degrees C.