The influence of the valence state of titanium in MgCl2‐supported titanium catalysts on olefin polymerization

The relationships between the valence state of titanium in MgCl2‐supported titanium catalysts and polymerization performances for ethylene and propylene were studied. When the titanium species of the supported titanium catalyst 1 was preliminarily reduced by treating it with AlEt3, the resulting catalyst system 2 had lost the activity for propylene polymerization completely. The catalyst activity for ethylene polymerization was found to be reduced to 20% of that of the original catalyst 1. In the AlEt3‐pretreated catalyst 2 no Ti4+ is found and 80% of the total titanium is present as Ti2+. The catalyst system 2 plus AlEt3, however, does exhibit activity towards ethylene‐propylene copolymerization, propylene insertion being possible if the end of the growing polymer chain is an ethylene unit. The titanium in the AlEt3‐reduced catalyst 2 could be oxidized again by treatment with various agents. The oxidized catalysts 3, in conjunction with freshly added AlEt3 as cocatalyst, are active for propylene polymerization and show increased activity for ethylene polymerization in relation to the extent of oxidation.