The roles of oxidation state,Lewis acid cocatalyst and solvent polarity in activating titanium compounds for olefin polymerization

The polymerization activity of the following three catalyst systems towards ethylene has been investigated and compared: 1) methyltitanocene chloride-Me₂AlCl 2) η³-allyltitanocene-Me₂AlCl and 3) titanium dichloride tetrahydrofuranate-Me₂AlCl. The first two catalysts formed homogeneous phases and produced linear polymer; the last catalyst functioned in a heterogeneous medium and formed crosslinked polymer. The titanium(IV) catalyst was about 30 times more active than the titanium(III) system and the titanium(II) catalyst on MgCl₂ could be made 8 times more active than the titanium(IV) system. A novel mechanism is proposed to explain the behavior and activity of the titanium(II) system.