Temperature effects Ziegler-Natta catalysts

In the broadest sense, Ziegler Natta catalysts may be regarded as combinations of Group IV-VIII transition metal compounds with Group I-III organometallics which can effect polymerization of olefins and dienes under relatively mild conditions of temperature and pressure [82,83]. Titanium compounds and aluminum alkyls are used most frequently in commercial polyolefin processes. Both titanium and vanadium compounds are used in conjunction with aluminum alkyls in catalyst systems for synthetic rubber/elastomers. 

Table 7). In an early application, VF was polymerized with a catalyst composed of diethylalnminnm bromide-titanium tetrachloride-carbon tetrachloride (82). A Ziegler-Natta system based on vanadyl acetylacetonate and AIR(OR)Cl compounds gives good yields (82) at polymerization temperatures up to 50°C. A modified catalyst prepared from vanadium oxytrichloride, triisobutylaluminum, and tetrahydrofnran was foimd to be the most effective Ziegler-Natta system... 

Commercial Ziegler polyethylene processes are generally operated at pressures only slightly above atmospheric, namely 2-4 atmospheres and at temperatures of 50—75°C. Polymerization is conducted in the presence of Ziegler-Natta catalysts, the nature of which is discussed in Chapter 1. For the polymerization of ethylene the catalyst is usually based on titanium tetrachloride/aluminium alkyl (e.g., diethylaluminium chloride). The catalyst may be prepared in situ by adding the components separately to the reactor as solutions in diluents such as diesel oil, heptane or toluene or the components may be pre-reacted and the catalyst added as a slurry in a liquid diluent. These operations must be conducted in an inert atmosphere (usually of nitrogen) since oxygen and water reduce the effectiveness of the catalyst and may even cause explosive decomposition. In a typical process, ethylene and the catalyst and diluent are... 

The polymer attributes are also effected by such process parameters as the reaction temperature, pre-activation of the catalyst and concentration of alkyls. Ziegler-Natta polymerization does not easily allow for secondary reactions to... 

Figure 1 Effect of multiple site types and mass and heat transfer resistances on the microstructure of polypropylene made with heterogeneous Ziegler-Natta and metallocene catalysts. The overall MWD and CCD are assumed to result from the superposition of individual MWDs and CCDs for three site t)rpes (T = temperature, M = number average molecular weight, = hydrogen, CjH = propylene, C2H4 = ethylene, Fj = molar fraction of propylene in copolymer, /(F,) == copolymer composition distribution, r = chain length, wix) = weight chain length distribution).

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