Titanium oligomerization

The structure of these products is uncertain and probably depends on pH and concentrations in solution. The hydroxyl or carboxyl or both are bonded to the titanium. It is likely that most, if not all, of these products are oligomeric in nature, containing Ti—O—Ti titanoxane bonds (81). Thek aqueous solutions are stable at acidic or neutral pH. However, at pH ranges above 9.0, the solutions readily hydroly2e to form insoluble hydrated oxides of titanium. The alkaline stabiUty of these complexes can be improved by the addition of a polyol such as glycerol or sorbitol (83). These solutions are useful in the textile, leather (qv), and cosmetics (qv) industries (see Textiles). 

The orange-red titanium acetylacetone chelates are soluble in common solvents. These compounds are coordinately saturated (coordination number equals 6) and thus much more resistant to hydrolysis than the parent alkoxides (coordination number 4). The alkoxy groups are the moieties removed by hydrolysis. The initial product of hydrolysis is beheved to be the bis-hydroxy bis-acetylacetone titanate, (HO)2Ti(acac)2, which oligomerizes to a... 

Titanium, tetrakis(trimethysilyl)oxy-, 3, 334 Titanium, tetranitrato-stereochemistry, 1,94 Titanium, triaquabis(oxalato)-structure, I, 78 Titanium, tris(acetylacetone)-structurc, 1,65 Titanium alkoxides oligomeric structure, 2,346 synthesis ammonia, 2, 338 Titanium chloride photographic developer, 6,99 Titanium complexes acetylacetone dinuclear, 2, 372 alkyl... 

Olefin metathesis technology, in polymer synthesis, 26 944-948 Olefin oligomerization, 16 111 Olefin oxides, alkanolamines from (with ammonia), 2 122-140 Olefin polymerization, organic titanium compounds in, 25 122 Olefin(ic) polymers, 17 699-709 ethylene-propylene elastomers, 17 705-707... 

The patent literature contains several references to the use of sulfoxide complexes, usually generated in situ, as catalyst precursors in oligomerization and polymerization reactions. Thus, a system based upon bis(acrylonitrile)nickel(0> with added Me2SO or EtgSO is an effective cyclotrimerization catalyst for the conversion of butadiene to cyclo-1,5,-9-dodecatriene (44). A similar system based on titanium has also been reported (407). Nickel(II) sulfoxide complexes, again generated in situ, have been patented as catalyst precursors for the dimerization of pro-pene (151) and the higher olefins (152) in the presence of added alkyl aluminum compounds. 

After reaching the desired DP, 40-50 % of the oligomeric melt is transferred to the polymerization vessel. Titanium butoxide (50-150 ppm) or dibutyl tin oxide catalyst (100-250 ppm), or some combinations of the two catalysts, is added to catalyze polymerization at 260-275 °C. A vacuum of <0.15 kPa is applied to remove the condensed water so as to drive the reaction until the polymer reaches an intrinsic viscosity (IV) of 0.7-0.9 dL/g. 

Carboxy-terminated oligomeric polyester compositions consisting of resorcinol, terephthalic isophthalic acid, diphenyl carbonate, and terephthalic acid catalyzed by titanium tetrabutoxide were prepared by Brunelle et al. (1) and used as thermosetting applications. 

A soluble titanium-based modified Ziegler-Natta catalyst [Ti(OR)4-Et3Al, R = n-Bu, isoPr] is employed in the reaction.42 Since similar catalysts may be used for the oligomerization and polymerization of ethylene, the nature and oxidation state of the metal and reaction conditions determine selectivity. Ti4+ was found to be responsible for high dimerization selectivity, whereas polymerization was shown to be catalyzed by Ti3+. According to a proposed mechanism,42,43 this catalyst effects the concerted coupling of two molecules of ethylene to form a metal-lacyclopentane intermediate that decomposes via an intramolecular p-hydrogen transfer ... 

Variations of this mechanism included the suggestion of a partially bonded alkene molecule,299 the participation of a titanium-aluminum ion pair,300 and a concerted alkene insertion.301 The development of the activator-alkyl mechanism was probably strongly influenced by the Aufbau reaction, studied originally by Ziegle.102 He observed that Group I—III alkyl compounds such as Et3Al catalyzed the oligomerization of ethylene to terminal alkenes. Additional evidence of such mechanism comes from the fact that alkylaluminum compounds exist in dimeric... 

On the basis of H NMR data it has not been possible to make any definite conclusions concerning the structures of oligomeric titanium and zirconium alkoxides. At room temperature only one set of CH2CH3 signals was observed for [Ti(OEt)4]4 and although the presumably rapid... 

Hydrolysis of Ti(OPr )4 does not allow the obtaining of ideal Ti02 powders [1394], In contrast to oligomeric titanium ethoxide and butoxide, titanium isopropoxide is a monomeric molecule condensation of its hydrolysis product occurs very quickly and results in quick nonuniform particle growth and minute particles quickly agglomerate into polydisperse species. 

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