Role of Dispersion State of Ti Species in Deactivation of MgCl_2-Supported Ziegler-Natta Catalysts

Deactivation behaviors of TiCl_3/MgCl_2 model catalysts with molecularly dispersed TiCl_3 were investigated to clarify the role of the dispersion state of the Ti species in the deactivation of MgCl_2-supported Ziegler-Natta (ZN) catalysts for propylene and ethylene polymerization. The propylene and ethylene polymerization activities of clustered Ti species supported on MgCl_2 were about one tenth of those of isolated Ti species, indicative of a significance of the aggregation of Ti species in the deactivation of ZN catalysts for olefin polymerization. Moreover, the time-course depression of the monomer consumption for the clustered Ti species was slower than that for the isolated Ti species in propylene polymerization, while the dispersion state hardly affected the depression rate in ethylene polymerization. The reduction rate of the Ti species was concluded as important for the time-course depression of propylene consumption, while ethylene polymerization was insensitive to the oxidation state of the Ti species