Titanium polymeric hydride

A model olefin polymerization catalyst previously characterized as [(C5H5)2TiAlEt2]2 has been studied by X-ray diffraction, H n.m.r., and mass spectral techniques. The compound contains (l- -CjHj) and/i(l- dimeric titanium-aluminium hydride structure (3) has been suggested. Alkyl exchange between a polymeric alkyl-titanium compound and alkylaluminium compound, present in excess, is... 

Al—Ti Catalyst for cis-l,4-PoIyisoprene. Of the many catalysts that polymerize isoprene, four have attained commercial importance. One is a coordination catalyst based on an aluminum alkyl and a vanadium salt which produces /n j -l,4-polyisoprene. A second is a lithium alkyl which produces 90% i7j -l,4-polyisoprene. Very high (99%) i7j -l,4-polyisoprene is produced with coordination catalysts consisting of a combination of titanium tetrachloride, TiCl, plus a trialkyl aluminum, R Al, or a combination of TiCl with an alane (aluminum hydride derivative) (86—88). 

It is known that the polymerization of ethylene by trialkyl aluminum is not a rapid reaction at normal pressures and temperatures. Ziegler, Gellert, Holzkamp, Wilke, Duck and Kroll (72) have found that ethylene was polymerized to higher trialkylaluminums only at elevated temperatures and pressures. Anionic hydride transfer commonly occured under these conditions. However, the addition of a transition metal halide such as titanium tetrachloride, the classical Ziegler catalyst, polymerized ethylene rapidly under mild conditions. 

As in the previous section, hydrogen increases the concentration of the active sites. Moreover, we think that the polymerization is preceded by the formation of a titanium hydride complex. If this is correct, hydrogen also increases the overall catalytic activity. The effects of hydrogen pressure on catalytic activity and molecular weight of SPS are summarized in Table 17.7. 

Ziegler-Naita caialysts consist of a combination of alkyls or hydrides of Group I-III metals with salts of the Group IV-VHI metals. The most generally efficient catalyst combinations are those in which an aluminum alkyl derivative is interacted with titanium, vanadium, chromium or zirconium salts. The most important application of these catalysts is in the polymerization of olefins and conjugated dienes. Not every catalyst combination is equally effective in such polymerizations. As a general rule, Ziegler-Natta combinations that will polymerize 1-olefins will also polymerize ethylene, but the reverse is not true. 

Termination occurs primarily through chain transfer to hydrogen, that is, hydro-genolysis of the R -Ti bond as in eq 3.7. The titanium hydride may add ethylene to produce another active center for polymerization. 

The polymerization of cyclopentadiene (5) was investigated in bulk and in solution with lithium aluminum hydride-titanium tetrachloride and lithium aluminum tetraoctyl-titanium tetrachloride catalyst systems. The polymerizations were carried out in nitrogen atmosphere using highly purified—i.e., freshly distilled— reactants. 

Additionally, if the initiation reaction is more rapid an the chain propagation, a very narrow molecular weight distribution, MJM = 1 (Poisson distribution), is obtained. Typically living character is shown by the anionic polymerization of butadiene and isoprene with the lithium alkyls [77, 78], but it has been found also in butadiene polymerization with allylneodymium compounds [49] and Ziegler-Natta catalysts containing titanium iodide [77]. On the other hand, the chain growth can be terminated by a chain transfer reaction with the monomer via /0-hydride elimination, as has already been mentioned above for the allylcobalt complex-catalyzed 1,2-polymerization of butadiene. 

For the polymerization to proceed at a reasonable rate, the use of a transesterification catalyst is needed. Compounds which are usually used as a catalyst for the preparation of polyesters through transesterification can be used here. These include lithium, sodium, zinc, magnesium, calcium, titanium, maganese, cobalt, tin, antimony, etc. in the form of a hydride, hydroxide, oxide, halide, alcoholate, or phenolate or in the form of salts of organic or mineral acids, complex salts, or mixed salts.(10) In this study, tetrabutyl titanate (TBT) in the amount of 1000 ppm was used normally. 

Use Tetraethyl and tetramethyl lead, titanium reduction, sodium peroxide, sodium hydride, polymerization catalyst for synthetic rubber, lab reagent, coolant in nuclear reactors, electric power cable (encased in polyethylene), nonglare lighting for highways, radioactive forms in tracer studies and medicine, heat transfer agent in solar-powered electric generators. 

Ziegler catalyst. A type of stereospecific catalyst, usually a chemical complex derived from a transition metal halide and a metal hydride or a metal alkyl. The transition metal may be any of those ingroups IV to VIII of the periodic table the hydride or alkyl metals are those of groups I, II, and III. Typically, titanium chloride is added to aluminum alkyl in a hydrocarbon solvent to form a dispersion or precipitate of the catalyst complex. These catalysts usually operate at atmospheric pressure and are used to convert ethylene to linear polyethylene and also in stereospecific polymerization of propylene to crystalline polypropylene (Ziegler process). 

Ethylene was polymerized [A. Schindler, J. Polym. Sci Part C, 4, 81 (1963)] in n-heptane with a catalyst system consisting of diisobutylaluminum hydride (1.5 mmol/L) and titanium tetrachloride (2.5 mmol/L). The catalyst components were reacted at these concentrations at 0°C and the mixture was then aged under a nitrogen blanket for 15 min. Ethylene was fed at 770 mm Hg pressure and the temperature of the catalyst suspension maintained at 40°C. It was found that the experimental data for the rate of polymerization could be represented best by assuming a mixed first and second-order dependence of the form... 

The A1 coordinates with the halogen on the titanium and activates it for insertion by removing electron density as in the polymerization reactions described in 5.8.2.3.5.ii.a. The titanium hydride reacts more easily with ethylene than with the higher 1-alkene present and forms the ethyltitanium complex. This complex then selectively inserts the... 

Hydrides and alkyls of the titanium triad metals are polymerization catalysts, so it is understandable that there are few stable r-allyl intermediates. The only example we can locate is the reaction between the zirconium hydride XIV and butadiene, which yields the homoallyl complex XV in place of the expected t-allyl complex ... 

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