Progress in the syndiotactic polymerization of styrene with metallocene/MAO catalysts

Metallocene/MAO catalysts are useful for the production of syndiotactic polystyrene - a new class of high performance polymers. The melting point of the obtained syndiotactic polystyrene depends on the metallocene used and can reach up to 275 degrees C. In the past, the most active catalysts in polymerization have been half-sandwich titanocenes such as CpTiCl3 and Cp*TiCl3. If the chlorinated compounds are changed into the fluorinated compounds as CpTiF3 and Cp*TiF3, the activity increases by a factor of 5 to 100. The fluorinated titanocenes are more stable at higher temperatures and need a lower MAO excess in order to obtain optimal activities. Polymers obtained with the unsubstituted CpTiF3 show melting points which are 17 degrees C lower than those synthesized by pentamethylcyclopentadienyltitaniumtrifluoride. Especially Cp*TiF3 shows a much higher activity and, compared with the chlorinated compound, gives polymers with a higher molecular weight. Substituted cyclopentadienyltitanocenes have even higher activities. Ethene/styrene copolymers can be obtained by catalysis with zirconocene compounds.