Preparation of syndiotactic polystyrene using the doubly bridged dinuclear titanocenes Seok Kyun Noh a, * , Sanghyun Kim a , Youngdo Yang a , Won Seok Lyoo b , Dong-ho Lee c a School of Chemical Engineering and Technology, Yeungnam University, 214-1 Daedong, Gyeongsan, Gyeongbook 712-749, South Korea b School of Textile, Yeungnam University, Gyeongsan, Gyeongbook 712-749, South Korea c Department of Polymer Science, Kyungpook National University, Taegu 702-701, South Korea Received 2 September 2003; received in revised form 9 October 2003; accepted 21 October 2003 Abstract As a new kind of dinuclear metallocene four DBDM (doubly bridged dinuclear metallocene) that hold two different bridging units linking two metallocenes have been prepared and their polymerization properties have been pursued. The selected bridging ligands for DBDM were polymethylene and dialkoxy terminated derivatives to bond two cyclopen- tadienyls and two titanium centers, respectively. The syntheses of new dinuclear metallocenes 5–8 were able to be achieved by the reaction between dinuclear half-titanocenes 1 and 2 and ditrimethylsiloxy terminated derivatives 3 and 4 at )78 °C. The EI mass spectra and 1 H and 13 C NMR spectral data were very informative to identify their formu- lations as well as structural features. The polymerization of styrene was conducted by using DBDM 5–8. From the polymerization studies it was found that (i) DBDM 7 and 8 holding 2,2-diethyl-1,3-dipropanoxy (DEP) bridge not only show greater activity but also produce higher syndiotactic polystyrene than DBDM 5 and 6 holding 1,1,4,4-tetramethyl- 1,4-dibutanoxy (TMB) bridge between two titanium centers, (ii) activities increase with increase in the polymerization temperature, the amount of cocatalyst and monomer concentration, (iii) the most crucial factor to control the ste- reoregularity of the resulting polystyrene is the styrene concentration in reaction system, (iv) surprisingly the catalyst structure does not have much effect on molecular weight of the obtained polystyrenes. The most significant feature from this study is that the second bridging dialkoxy terminated ligands connecting two titanium centers likely exert more pronounced influence than the polymethylene bridges between two Cp groups on the activity of the catalyst as well as the stereochemistry of the generated polymers. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Dinuclear metallocene; Doubly bridged metallocene; Styrene polymerization; Syndiotactic polystyrene 1. Introduction Since the discovery of Kaminsky and Sinn in 1980, that metallocene complexes can be activated by meth- ylaluminoxane (MAO) cocatalyst and used as organo- metallic catalysts to polymerize a-olefins, styrene, and polar monomers [1–4]. These catalysts led to an out- standing enhancement of the polymerization activity in combination with cocatalyst as well as to an important increase in the uniformity of the molecular weight dis- tribution of polymers obtained. Such advantages led to a significant increase in research intensity in metallocenes itself and its derivatives as a new kind of catalyst to allow the synthesis of highly stereoregular polypropyl- enes, ethylene copolymers with a higher content of * Corresponding author. Tel.: +82-538-102-526; fax: +82- 538-148-790. E-mail address: sknoh@yumail.ac.kr (S.K. Noh). 0014-3057/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2003.10.010 European Polymer Journal 40 (2004) 227–235 www.elsevier.com/locate/europolj