Reaction of Ziegler-Natta centres with monomers

5 REACTION OF ZIEGLER-NATTA CENTRES WITH MONOMERS 

According to Cossee, the isotactic centre has one and the atactic two vacancies. According to Rodriguez, the organometal is coordinated into one of the two vacancies of the isotactic centre. The addition of donors (diethyl ether, triethylamine, pyridine, etc.) greatly affects the polymerization rate (catalyst activity) as well as the ratio of the stereoregular and atactic product components. Donors affect the structure of active centres and modify it. 

According to present ideas, the initiation mechanism of diene polymerization on ZN centres does not substantially differ from that of alkene initiation. Experiments support the idea according to which the chain is propagated on the transition metal atom it may be bound to the metal either by a a, or by a n allylic bond 

All the findings collected to date do not enable us to formulate a detailed initiation mechanism for the polymerization of alkenes and dienes on ZN centres. The initiation and growth mechanisms are usually combined in a single scheme which will be discussed in detail in Chap. 5, Sect. 4. 

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Reaction of Ziegler-Natta centres with monomers. 

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