Ziegler third generation

The property envelope of polyolefins has been expanded by the direct synthesis, in the reactor, of novel alloys and blends with a balance of properties not possible ftom conventional, third-generation catalyst polymerization. Such advances in Ziegler-Natta polymerization technology show that polyolefin-based resins can continue to provide the most cost-effective solutions for a wide and ever-increasing range of plications in the global plastics market. 

To recap, there are two types of donors, internal and external. For the third-generation catalysts the internal/external pair is an ester/ester pair, while for the fourth-generation it is the phthalate/alkoxy silane pair. The fifth-generation Ziegler-Natta catalysts are comprised of an internal donor, which is a diether compound and may be used with or without the additional external donor (see Table 9). 

Organic Lewis bases are widely used as electron donors in the third generation supported Ziegler-Natta catalysts for alpha-olefin polymerization to enhance activity and to improve stereospecificity. These catalysts comprise a solid catalyst, MgCl2/TiCl4/electron donor (-ED), and a cocatalyst, an aluminium alkyl usually complexed with an electron donor. 

Ziegler-Nai ta catalyst development did not stop with the introduction of the high yield, high isotactic third generation catalyst process. The supersetive catalyst has provided the basis for a versatility in product and process development never previously thought possible. This system meets the four major objectives vital for the control of polyolefin properties. 

The effectiveness of the third generation, superactive Ziegler-Natta catalyst is dependent on reproducible dispersion of the active sites on the support as well as the chemical and physical properties of the support itself. The five basic indispensable requirements for this superactive catalyst are ... 

It is worth noting that, to obtain efficient supported Ziegler-Natta catalysts of the third and fourth generation, it is TiCU rather than preformed TiCL that is supported. When TiCl3 was supported on MgCl2 (e.g. by deposition from the solution of a TiCl3.3Py complex) and then activated with an alkylaluminium compound, the obtained catalyst appeared to be aspecific for propylene polymerisation [69], However, it could be converted into an isospecific catalyst by adding a Lewis base such as ethyl benzoate [70],... 

TABLE 8.4. Third- and Fourth-Generation Ziegler-Natta Cataly sts (1977/1983). 

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