THE NATURE OF POLYMERIZATION CATALYSTS PREPARED FROM METAL ALKYLS AND TITANIUM HALIDES

Abstract

A study has been made of the composition and structure of the insoluble complexes formed in the reaction of aluminum triisobutyl or lithium n-butyl with titanium tetrachloride or trichloride in heptane at room temperature by chemical and X-ray diffraction analyses. For the tetrachloride systems it has been shown that, with metal alkyl:titanium tetrachloride ratios of 0.5 to 4, at least 50% of the titanium is present in the tetravalent state and that there is considerable loss of chlorine and alkyl groups. The aluminum complexes are amorphous except at component ratios of 0.5 to 1, where the X-ray pattern indicated traces of titanium trichloride.With the aluminum triisobutyl–titanium trichloride system, X-ray evidence has shown that the titanium trichloride remains essentially unchanged. This result, together with the low aluminum content (less than 0.5%), is consistent with Natta's suggestion that this catalyst for define polymerization consists of a trichloride surface on which small quantities of aluminum alkyl are chemisorbed.The reaction between lithium butyl and titanium trichloride at ratios above unity results in the formation of a new crystalline compound having a sodium chloride type lattice with a lattice spacing of 5.20 Å. The compound is thought to be a double salt of the type (LiCl)_n.TiCl₂ or (LiCl)_n.TiCl. Evidence of a second crystalline component was also noted but it could not be identified.Tentative reaction schemes are proposed for the formation of the various complexes and their structures are considered in relation to their ability to polymerize 1-butene.