ESR study on MgCl_2-supported half-titanocene catalyst for syndiospecific polymerization of styrene

摘要

The MgCl_2-supported CpTiCl_3 catalysts with different Ti content were prepared and used for syndiospecific polymerization of styrene. These catalysts were investigated by means of electron spinning resonance (ESR) spectroscopy. It is found that there exist two kinds of active species in this catalytic system. One is a specific active site and cannot be removed into the solution by MAO. The other one is readily removed into the solution during the interaction with MAO, and the same active site as that in the CpTiCl_3-MAO homogeneous system is formed. The MgCl_2 supported CpTiCl_3 catalyst was also compared with the SiO_2/CpTiCl_3-MAO system. The data show that the CpTiCl_3 supported on the MgCl_2 surface is more difficult to be removed by MAO than the active site immobilized on the SiO_2 surface, leading to the lower activity of MgCl_2/CpTiCl_3-MAO system and lower syndiotacticity of obtained polystyrene.