Zirconium acetylacetonate, effect

The solvents most frequently mentioned as dissolving the metal acetylacetonates are benzene, ethanol, chloroform, carbon tetrachloride, carbon disulfide, and petroleum ether. Since the solubility in petroleum ether is much less than in benzene, the former is frequently added to a saturated solution in the latter to effect crystallization. Hatch and Sutherland13 give data on the solubilities of sodium, potassium, magnesium, beryllium, and aluminum acetylacetonates in benzene, cyclohexane, and n-hexane from 0 to 100°. Other solubility measurements are as follows copper(II) acetylacetonate, 0.00338 mol/1. in benzene at 25° 57 zirconium acetylacetonate, 200, 34, 47, and 56 g./l. in absolute ethanol, carbon disulfide, carbon tetrachloride, and acetylacetone, respectively, at 25°.4 Recent data by Blanch58 are assembled in the following table. 

The process is initiated at terminal hydroxy groups and favoured by the spiral-like structure of polysiloxanes. Replacement of the hydroxy groups by methyl, or blocking them by chelation to copper, iron or zirconium acetylacetonates, considerably decreases the rate of decomposition of the polymer and increases its thermal stability (Table 9). However, pronounced crosslinking even at moderate temperatures was observed in the polymer stabilized by transition metal compounds. The effect of the metal additives during thermal ageing is associated with reactions leading... 

At this point Ziegler and his coworkers carried out experiments on the effects of adding various other metal compounds to triethylaluminum. In one of these experiments with zirconium acetylacetonate, ethylene, and triethylaluminum, they found, to their surprise, an autoclave filled with a solid cake of snow-white polyethylene (1. ) Further work revealed that aluminum alkyls in conjunction with certain transition metal compounds of Groups IV-VI, as well as uranium and thorium, were active ethylene polymerization catalysts. Ultimately, Ziegler catalysts were described to be the product of reaction of metal alkyls, aryls, or hydrides of Groups I-IV and certain transition metal compounds of Groups IV-VIII (Reaction 4). The choice of a particular catalyst and experimental conditions is dictated by the structure of the monomer to be polymerized. 

Following the discovery of the a-olefin synthesis, a systematic investigation of metal compounds was undertaken. In 1953, zirconium acetylacetonate was used as a cocatalyst. Instead of liquid a-olefins, a voluminous white precipitate was produced. This new substance was a polymer of ethylene. Ten years later, millions of pounds of this Ziegler-type polyethylene were made in the United States alone. In addition to the zirconium compound, other transition metal compounds were found to be effective cocatalysts. Today titanium tetrachloride or trichloride is used as the cocatalyst with an organoaluminum compound. 

Silica/chromia catalysts have also been modified by the incorporation of other oxides such as alumina" or zirconia," by impregnating a silica support with zirconium acetylacetonate or aluminum sec-butoxide or co-gelling the silica gel with appropriate soluble salts. Zirconia-modified catalysts are similar to those with added titanium in their effect but have not been widely reported. Aluminum-modified catalysts have increased activity and provide lower-molecular-weight polymers, but the procedure for their preparation is complicated. Neither type of catalyst is widely described in the literature but they are reported as containing different active sites." ... 

Other catalysts effective in the conversion of isocyanates into carbodiimides include the naphthenates of Mn, Fe, Co, Cu and Pb, derivatives of metallic acetylacetonates, the alkoxides of titanium, zirconium and niobium and vanadium oxides or chlorides. Sterically hindered isocyanates are readily converted into carbodiimides upon heating in the presence of a catalytic amount of a strong base. For example, heating of... 

The metal acetylacetonates and their pyridine complexes were used as catalysts in the epoxy-novolac systems [310-320]. These compounds improved the mechanical strength of the polymers [310,312], but the titanium and zirconium chelates also advanced the adhesive strength and the water resistance [319]. The investigation of the effect of the acetylacetonates on the interaction of the epoxy oligomers with the phenolformaldehyde resins showed that the catalytic activity of the metal cations diminishes in the series [Eq. (2)]... 

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