Post Ziegler and Natta Coordination Polymerization of Olefins

4 Post Ziegler and Natta Coordination Polymerization of Olefins 

In the current industrial practice, coordinated anionic catalysts differ considerably from the original ones, developments by Ziegler, Natta and others. Using the same basic chemistry, new compounds were developed over the years that yield large quantities of polyolefins from small amounts of catalysts. In addition, catalysts can now be designed to yield products that are either wide or narrow in molecular weight distribution, as needed [312]. The multinuclear olefin polymerization catalysts 

Products from reactions of tiivalent alkoxy chlorides of transition metals with certain halogen-free organoaluminum compotmds, e.g., tiiisobutylaluminum. Such catalysts are used without any support. 

Products from reactions of magnesium compounds with titanium compounds. In these catalysts the transition metals are attached chemically to the surfaces of solid magnesium compounds. The reactions take place between the halogen atoms from titanium compounds and the hydroxyl groups at the surfaces of magnesium hydroxide  

Titanium compounds bonded to the surface OH groups of Mg(OH)2 are mainly inactive. The active sites are the ones associated with the coordinated and unsaturated negative oxygen ions [317]. Reactions with aluminum alkyls activate the catalysts [312]. For high efficiency, special carriers must be used together with a correct balance of the reactants, and proper reaction conditions. Some choice combinations are [312] Mg(OH)Cl with TiC MgCl2 3Mg(OH 2 with Ti(OR) ,Cl , MgS04 3Mg(OH)2 with Ti(OR) ,Cly and Mg(OH 2 with TiCL,. 

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