Supported Half-sandwich Metallocene Catalysts

Conjugated dienes have been polymerised using supported half-sandwich metallocene catalysts. For instance, catalysts derived by supporting CpTiCl3 on alumina-silica gels, containing—0-Ti(Cp)Cl2 species, displayed activity in isoprene polymerisation without the addition of any other activator. Depending on the alumina-silica gel composition, the kind of polymerisation medium and the temperature, these catalysts exhibited various activities and selectivities polyisoprenes with a predominant 3,4 structure and mixed 1,2/ trans-1,4 structure were obtained [118,119], 

It is interesting that the presence of the alumina-silica carrier in the catalyst is sufficient enough for the activation of the titanocene for the polymerisation, similarly like the presence of methylaluminoxane in the titanocene homogeneous polymerisation system CpTiCl3 alone does not exhibit catalytic activity in conjugated diene polymerisation. 

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When supported on AI2O3 as a carrier, half-sandwich metallocenes such as CpTiCl3 and Cp TiCl3 also gave rise to suitable stereospecific catalysts that could even be activated by Al(z -Bu)3 [69]. However, in contrast to the respective homogeneous catalysts (yielding syndiotactic polystyrene), polymerisation with these heterogeneous catalysts afforded isotactic and syndiotactic polystyrenes. 

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