Olefin polymerization, catalysis Ziegler-Natta

Much effort has been devoted during the last 30 years toward understanding the mechanisms operative in the coordination catalysis of ethylene and a-olefin polymerization using Ziegler-Natta systems (metal halide and aluminum alkyl, sometimes with Lewis base modifiers). Aspects of the complex heterogeneous reactions have been elucidated (jL- ) but the intimate mechanistic detail - for example the role of inhibitors and promoters, kinetics and thermodynamics of chain growth, modes of chain transfer and termination - comes primarily from studies of homogeneous catalysts ... 

The study of catalytic polymerization of olefins performed up to the present time is certain to hold a particular influence over the progress of the concepts of the coordination mechanism of heterogeneous catalysis. With such an approach the elementary acts of catalytic reaction are considered to proceed in the coordination sphere of one ion of the transition element and, to a first approximation, the collective features of solids are not taken into account. It is not surprising that polymerization by Ziegler-Natta catalysts is often considered together with the processes of homogeneous catalysis. 

The involvement of the a-elimination reaction in this cycle has been in question following experiments on cyclopentadienyl cobalt complexes, where evidence for olefin insertion for Ziegler-Natta polymerization catalysis has been obtained by labelling experiments, using C2H4 with a deuterated cobalt complex (70) ... 

Breakthroughs in single-site catalysis have completely transformed our view of alpha-olefin polymerization catalysis. The conventional Ziegler—Natta catalysts used in industrial production of polyolefins... 

An Organometallic Com pound That Occurs Naturally Coenzyme B,2 591 Organocopper Reagents 592 Palladium-Catalyzed Cross-Coupling 595 Homogeneous Catalytic Hydrogenation 597 Olefin Metathesis 600 Ziegler-Natta Catalysis of Alkene Polymerization 603 Summary 606 Problems 608... 

Key words Olefin polymerization, Ziegler-Natta catalysis... 

Under the reaction conditions employed, the oligomerization is living the aluminium is removed from the chain in a separate process step [2]. Further research on the Aufbau reaction led to the discovery of transition metal catalyzed olefin polymerization (Ziegler-Natta catalysis) [3]. 

Coose P, Ziegler-Natta Catalysis I Mechanism of Polymerization of a-Olefins with Ziegler-Natta Catalyst, J Catal, 3, 80 (1964)... 

The great industrial importance of the polymerization of olefins with Ziegler-Natta catalysis has stimulated a lot of research, on a more or less empirical basis in the major manufacutring companies and still does today. 

Stereospecific Polymerization. It was found quite early in the development of Ziegler-Natta catalysts that stereospecific polymerization usually requires the presence of a crystalline catalyst surface—i.e, heterogeneous catalysis. Most recently, this has been confirmed in the careful examination of catalyst surfaces by Rodriguez, van Looy, and Gabant (35). It must be remembered, however, that this work dealt largely with a-olefins. 

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