Triethylaluminium-titanium tetrachloride

Ziegler catalysts studied for the oligomerisation of a-olefins tend to be based on modified first-generation catalysts, i.e. triethylaluminium/titanium tetrachloride. The aluminium/fitanium ratio has a marked effect on product properties, at less than 0.8 1, liquids were produced, whereas at ratios above 1 1, waxy products were obtained [6, 7]. This effect is believed to relate to changes in the catalysis mechanism, from cationic to anionic with higher proportions of aluminium. 

A typical Ziegler-Natta catalyst is the complex prepared from titanium tetrachloride and triethylaluminium. It is fed into the reaction vessel first, after which ethylene is added. Reaction is carried out at low pressures and low temperatures, typically no more than 70 °C, with rigorous exclusion of air and moisture, which would destroy the catalyst. The poly(ethylenes) produced by such processes are of intermediate density, giving values of about 0.945 g cm. A range of relative molar masses may be obtained for such... 

Furukawa et al. [274] and Natta cl al. [275,276] succeeded independently in the preparation of crystalline polyacetaldehyde by using some organometallic compounds, such as diethylzinc or triethylaluminium, for the low-temperature polymerisation of acetaldehyde. Metal alkyls and metal alkoxides, e.g. aluminium isopropoxide, zinc ethoxide or ethyl orthotitanate, have also polymerised other aldehydes such as propionaldehyde and trichloroacetaldehyde to give crystalline polymers (Table 9.3) [270,275,277], A highly crystalline isotactic polymer has been obtained from the polymerisation of w-butyraldehyde with triethylaluminium or titanium tetrachloride-triethylaluminium (1 3) catalysts. Combinations of metal alkyl, e.g. diethylzinc, with water [278] or amine [279] appeared to give very efficient catalysts for aldehyde polymerisations. 

The formation of linear isotactic or syndiotactic polymers can be achieved by metal-catalysed polymerisation. This employs Ziegler-Natta catalysts, made from triethylaluminium (Et3Al) and titanium tetrachloride (TiCl4), which react with alkenes by a complex mechanism. The polymerisation of ethylene (CH2=CH2) leads to the formation of (linear) high-density polyethylene, which is of greater strength than the (branched) low-density polyethylene produced on radical polymerisation. 

A typical Ziegler-Natta catalyst is the complex prepared from titanium tetrachloride and triethylaluminium. It is fed into the reaction vessel first, after which ethylene is added. Reaction is carried out at low pressures and low temperatures, typically no... 

By treatment of these materials with titanium tetrachloride valuable supported catalysts for the propene Ziegler-Natta type polymerization were obtained. These catalysts were tested by slurry polymerization using triethylaluminium as cocatalyst and showed an interesting activity compared with that exhibited by a commercial catalysts. The polymer products were also characterized by measuring the molecular weight distribution by gel permeation chromatography technique. 

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