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

Abstract

Abstract The relationships between the valence state of titanium in MgCl 2 ‐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 AlEt 3 , 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 AlEt 3 ‐pretreated catalyst 2 no Ti 4+ is found and 80% of the total titanium is present as Ti 2+ . The catalyst system 2 plus AlEt 3 , 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 AlEt 3 ‐reduced catalyst 2 could be oxidized again by treatment with various agents. The oxidized catalysts 3, in conjunction with freshly added AlEt 3 as cocatalyst, are active for propylene polymerization and show increased activity for ethylene polymerization in relation to the extent of oxidation.