Alkylaluminum titanium tetrachloride catalysts

Preformed Alkylaluminum-Titanium Tetrachloride Catalysts for the Polymerization of Isoprene... 

However, Natta, Pasquon, Zambelli and Gatti (63) have shown that titanium trichloride-dialkylaluminum chloride or titanium trichloride and alkylaluminum dichloride with nucleophilic materials are good catalysts for the polymerization of propylene to the isotactic structure. The titanium trichloride could also be made in situ from titanium tetrachloride and triethyl aluminum. Vesely, Ambroz, Vilin and Hamrik (64) showed the addition of the nucleophilic materials to diethylaluminumchloride-titanium trichloride polymerizations decreased the rate of polymerization and changed the stereospecificity. The more nucleophilic materials such as sulfur compounds were more effective than the less nucleophilic oxygen materials. 

Catalyst Preparation. Details of the equipment and procedures used were described earlier (13). Essentially, a 2M solution of the alkylaluminum compound in heptane was added gradually to a vigorously stirred 0.38M solution of titanium tetrachloride in a 2-liter Morton-type flask at 20° C. After a desired molar ratio of Al/Ti was reached, an aliquot of the catalyst slurry was withdrawn for testing. The addition of the aluminum compound was then resumed, and the operation was repeated at successive Al/Ti ratios. 

The catalysts studied here were preformed by the gradual addition of the alkylaluminum compound to a solution of titanium tetrachloride. This preparation method was found earlier (13) to give highly reproducible results. An Al/Ti mole ratio range of 0.60 to 2.0 or higher was usually covered. Each... 

Ziegler-Natta catalysts, which are of many different formulations, are organ ometallic transition-metaJ complexes prepared by treatment of an alkylaluminum with a titanium compound. Triethyl aluminum and titanium tetrachloride form a typical preparation. 

Alkylaluminums have become very important as mixed catalysts for low-pressure polymerization of olefins (especially ethylene), a reaction discovered by Ziegler and his colleagues.263 Numerous investigations have been devoted to a study of the mechanism of this reaction e.g., it has been shown that an important role in the polymerization is played by the organotitanium compounds formed from mixtures of alkylaluminums and titanium tetrachloride.264... 

The reduction of titanium tetrachloride by an equimolar quantity of alkylaluminum gives /S-TiCls, one of several crystalline modifications of the trichloride (Natta et al., 1961a). For example, Natta et al. (1959c) found that (C2H5)3A1TiCU at Al/Ti = 1.0-1.3 produced the form almost quantitatively. This catalyst yielded a polybutadiene composed of about 50% cis-1, 4-polybutadiene, 40% imns-l,4-poly butadiene, and 10% 1,2-... 

Karapinka, Smith, Carrick (79) studied the use of methyltitanium trichloride as a catalyst for polyethylene. Alone it was inactive for the polymerization of polyethylene. It required the predecomposition to titanium trichloride at 120° or the addition of titanium trichloride to produce an active catalyst. Vanadium tetrachloride also produced an active catalyst. Aluminum bromide failed to activate the catalyst, whereas trialkylaluminum which reacts to produce alkylaluminum chlorides was effective. 

Homogeneous catalysts, which polymerize only ethylene effectively, have been prepared from alkylaluminum compounds and bis fcyclopentadienyl) titanium dichloride (Breslow and Newburg, 1959 Natta and Mazzanti, 1960). Another soluble catalyst made from tetraphenyltin, aluminum bromide, and vanadium tetrachloride was reported by Garrick et al. (1960). 

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