Synthesis of new homogeneous metallocene-based olefin polymerization catalyst

Abstract

A new type of catalyst for the syndiospecific polymerization of styrene, $Cp^*Ti(TEA)$ (TEA = N($CH_2CH_2O)_3$) was prepared by either the reaction of triethanolamine with $Cp^*TiCl_3$ in the presence of triethylamine or the reaction of (TEA)TiCl with $LiCp^*$. The former reaction route is more efficient in terms of yield and easy accessibility of a starting titanium compound. The X-ray structure of $Cp^*Ti(TEA)$ reveals that $Cp^*Ti(TEA)$ exists as monomeric form in the solid state and the Ti atom adopts essentially an $\eta^5$ bonding posture with Cp* ring and a tetradentate bonding mode with triethanolateamine ligand via a transannular interaction from the bridgehead N atom to Ti. The compound $Cp^*Ti(TEA)$ is air and thermally stable, and soluble in hydrocarbon solvents. The catalytic system $Cp^*Ti(TEA)$/MMAO is more efficient than $Cp^*TiCl_3$/MMAO in producing highly syndiotactic polystyrene in terms of activity, conversion, stereospecificity, and Tm at all polymerization temperatures. $Cp^*Ti(TEA)$/MMAO catalytic system could conduct syndiospecific homopolymerization of styrene containing silyl-protected alcohol and tertiary amines as manifested by the preparation of syndiotactic polymers of 4- tert-butyldimethylsilyloxystyrene, 4-dimethylaminostyrene, and 4-diethylaminostyrene. Their solubility in organic polar solvents and the high thermal stability indicate that the advantages of the functionalization of the styrene, the preservation of the desirable physical property of the original polymer as well as the development of the new chemical property, were achieved. The chemical transformation of polymer gave a new syndiotactic polar polymer, poly(4-hydroxystyrene) which has never been obtained by traditional methods. In addition, the reaction of syndiotactic poly(4-diethylaminostyrene) with HCl afforded a new syndiotactic poly(4-diethylaminostyrene hydrochloride). The half-sandwich metallocene catalyst for the polymerization of ethylene, $Cp^*M(TEA)...