Titanium chlorides, Ziegler catalyst

Synthesis of linear polyethylene and coordinate polymerisation (combination of trialkyl aluminium and titanium chloride as catalyst) by Ziegler Isotactic and syndiotactic polymerisation (polypropylene and polydienes) discovered by Natta... 

Ziegler-Natta polymerization Stereospecific polymerization of olefines using a Ziegler catalyst. See titanium(IIl) chloride. 

Natta catalyst. A stereospecific catalyst made from metal alkyls and titanium chloride developed by the chemist Giulio Natta. See also Ziegler-Natta catalyst. 

Therefore, in such heterogeneous polymerizations, almost all industrial catalysts are supported, for example on silica, whereas the typical Ziegler s titanium catalysts are by definition supported on magnesium chloride. These catalysts are adsorbed at the surface or incorporated into the crystal structure of the support. Other catalysts, such as Phillips chromium catalysts, can be coupled at the support surface by a chemical bond. 

Tracer studies have been used in an attempt to determine the nature of the ends of the chain but these were as unsatisfactory as for propylene. Feldman and Perry (83) used triterated methanol to react the polyethylene from a titanium tetrachloridetrialkylaluminum catalyst. They found a continual increase in the number of polymeric chain ends which react with the tritium. This agrees with the results of Roha and Beears (84) who showed the very rapid exchange of alkyls which took place when ethylene was grown on a Ziegler catalyst in the presence of excess alkylaluminum chloride. In these experiments only an extremely small... 

ZIEGLER CATALYST. A type of stereospedfre catalyst, usually a chemical complex derived from a transition metal halide and a metal hydride oi a metal alkyl. The transition metal may be any of those in gioups IV to VIII of the periodic table the hydride or alkyl metals are those of groups I, II. and III. Typical, titanium chloride is added to aluminum alkyl in a hydrocarbon solvent to form a dispersion or precipitate of ilie catalyst complex. These catalysts usually operate at atmospheric pressure and are... 

Table VI summarizes important homogeneous Ziegler catalysts. The best known are the systems based on bis(cyclopentadienyl)titanium(IV), titanium alcoholates, vanadium chloride, or chromium acetylacetonate with trialkylaluminum or alkylaluminum halides.

In reporting a Ziegler-Natta catalyst, the kind of transition metal compound should not be omitted. Group 4-8 transition metal compounds, such as halides, oxyhalides, alkoxides, acetylacetonates, etc., have been used as catalyst precursors with activators such as alkyl derivatives or hydrides of group 1-4 metals. Titanium chlorides and triethylaluminium are most commonly applied for the preparation of heterogeneous catalysts in an aliphatic hydrocarbon medium. Also, vanadium oxychloride or acetylacetonate and dialkyaluminium chloride are often used for the preparation of homogeneous catalysts in an aliphatic hydrocarbon or an aromatic hydrocarbon medium. 

Thus, the experimental data show that the composition of catalytic systems does not influence the stereoregularity of the corresponding polymer fractions but only their relative content. Hence, the stereospecificity of the active centers of these catalysts is the same including the one-component catalyst TiCl2. This confirms the concepts on the monometallic character of AQ in the Ziegler-Natta catalysts. The possible existence of chiral titanium atoms on the titanium chloride surface was studied by Cossee and Arlman ... 

The exact nature of the Ziegler catalysts is somewhat obscure. The essential features seem to be that the TiCU (a covalent liquid, soluble in hydrocarbon solvents) is alkylated by the trialkylaluminum and also at least partly reduced to titanium (III). Titanium(III) chloride is an ionic solid, insoluble in organic solvents, so it is not surprising that the material so formed is not readily soluble in the reaction medium. This material, which is apparently somewhat variable in structure and composition but which contains Al as well as Ti, can add an olefin molecule at a Ti center, presumably in much the same way that ethylene adds to platinum (II) chloride to form Zeise s salts (Section 18.2), and an alkyl group already present on the Ti can then migrate onto the olefin to form a new, longer alkyl group ... 

Two years later, in October of 1953, another accidental discovery was made by Karl Ziegler of the Max-Planck Institut, Mulheim, Germany [10]. His catalyst consisted of titanium chloride combined with aluminum alkyl. The first patents were filed quickly, on October 17,1953. A polymer density of about 0.94 g mL 1 was reported. Ziegler licensed it within a year, offering only a laboratory method that each licensee then had to develop and scale up independently. Hoechst was one of the first licensees. One of the early problems, which was apparently not addressed in the license, was how to control the MW of the polymer [2]. 

The first generation of catalysts based on titanium tetrachloride or different modifications of titanium trichloride and ethyl-, isobutyl-, isoprenyl-, or chloride containing aluminum compounds, Ziegler catalysts, (Table 1) was characterized by low polymerization activity. Kinetic studies and applications of various methods have helped to define the nature of the active center . ... 

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