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The deactivation behaviors of TiCl3/MgCl2 model catalysts with molecularly dispersed TiCl3 were investigated to clarify the role of the dispersion state of the Ti species in the deactivation of MgCl2-supported Ziegler-Natta (ZN) catalysts for propylene and ethylene polymerization. The propylene and ethylene polymerization activities of clustered Ti species supported on MgCl2 were approximately one tenth of those of isolated Ti species, which is indicative of the significance of the aggregation of Ti species in the deactivation of ZN catalysts for olefin polymerization. Moreover, the time-course depression of monomer consumption for the clustered Ti species was slower than that for the isolated Ti species in propylene polymerization, whereas the dispersion state barely affected the depression rate in ethylene polymerization. The reduction rate of the Ti species was concluded to be important for the time-course depression of propylene consumption, whereas ethylene polymerization was insensitive to the oxidation state of the Ti species.

The dispersion state of surface Ti species is one of the most important factors for polymerization properties of MgCl_2-supported heterogeneous Ziegler-Natta catalysts. In this paper, ethylene-propylene copolymerization was conducted using a novel Ziegler-Natta model catalyst having “isolated” and “clustered” TiCl_3 molecules on MgCl_2. At a lower ethylene/propylene feed ratio, the dispersion state of the Ti species was found to stronglyaffect both the composition and sequence distribution of copolymers. The “isolated” Tispecies gave a relatively random copolymer and clustering of Ti species obviously enhanced the blockiness. The addition of an external donor basically deteriorated the random copolymerization character of the “isolated Ti species, but the degree of the deterioration depended on the kind of donors. On the contrary, the balance between themonomer feed and consumption dominated the copolymerization performance at a higher ethylene/propylene feed ratio to obscure the effects of the dispersion state.