Catalysis of olefin and diene polymerization

A significant event in the period covered by the present survey was the ACS conference on anionic polymerization in 1980 - the first major conference on the subject for many years. The abstracts of the papers presented at that meeting are available and a book containing the full texts is in preparation. A review of anionic polymerization has been written by Richards. A review of organolithium catalysis of olefin and diene polymerization, which contains some previously unpublished results, has also appeared. ... 

The advent of the energy crisis has caused us to examine traditional views of the relative costs of different monomers and to consider the potential of less costly monomers for polymerization. One can expect that catalysis of the coordinated anionic type will play a major role in any new developments in olefin and diene polymerizations. Finally, one should recall that Ziegler catalysts have found many uses in other areas of chemistry such as metathesis of olefins, oligomerization, isomerization, hydrogenation, and alkylation. The vast scope of these catalysts will almost certainly achieve a wider range as these types of studies continue in the future. 

Olefin metathesis has quickly become one of the most widely used methods for mild carbon-carbon bond formation in organic synthesis [1,2]. With the development of highly active, fimctional group-tolerant catalysts, like Grubbs second generation catalyst ([Ru] ), metathesis has been successfully applied across many areas of research, and some reviews already exist that deal with metathesis catalysis and applications [1-5]. This review focuses on recent developments in acycUc diene metathesis (ADMET) polymerization chemistry and methodology that have been published over the past five years, starting with a short discussion on the history of olefin metathesis and ADMET polymerization. 

Among the most significant developments in the field of catalysis in recent years have been the discovery and elucidation of various new, and often novel, catalytic reactions of transition metal ions and coordination compounds 13, 34). Examples of such reactions are the hydrogenation of olefins catalyzed by complexes of ruthenium (36), rhodium (61), cobalt (52), platinum (3, 26, 81), and other metals the hydroformylation of olefins catalyzed by complexes of cobalt or rhodium (Oxo process) (6, 46, 62) the dimerization of ethylene (i, 23) and polymerization of dienes (15, 64, 65) catalyzed by complexes of rhodium double-bond migration in olefins catalyzed by complexes of rhodium (24,42), palladium (42), cobalt (67), platinum (3, 5, 26, 81), and other metals (27) the oxidation of olefins to aldehydes, ketones, and vinyl esters, catalyzed by palladium chloride (Wacker process) (47, 48, 49,... 

The catalysis of the stereospecific polymerization of conjugated dienes is of considerable interest from both the scientific and the industrial points of view [1,2]. From butadiene and isoprene, as the industrially most important 1,3-dienes, in comparison with the polymerization of olefins many more structurally different stereoregular polymers can be derived cf the structures of the stereoregular polybutadienes and polyisoprenes given in Scheme 1 [106]. 

The essential characteristic of Ziegler-Natta catalysis is the polymerization of an olefin or diene, using a combination of a transition metal compound and a base metal alkyl cocatalyst, normally an aluminum alkyl. The function of the cocatalyst is to alkylate the transition metal, generating a transition metal-carbon... 

Olefin metathesis (OM) has proven to be one of the most important advances in catalysis in recent years based on the application of this chemistry to the synthesis of polymers and biologically relevant molecules [1-10]. This unique transformation promotes chain and condensation polymerizations, namely ring opening metathesis polymerization and acyclic diene metathesis polymerization (ADMET). Applications of metathesis polymerization span many aspects of materials synthesis from cell-adhesion materials [11] to the synthesis of linear polyethylene with precisely spaced branches [12]. 

Most addition polymerizations involve vinyl or diene monomers. The opening of a double bond can be catalyzed in several ways. Free-radical polymerization is the most common method for styrenic monomers, whereas coordination metal catalysis (Zigler-Natta and metallocene catalysis) is important for olefin polymerizations. The specitic reaction mechanism may generate some catalyst residues, but there are no true coproducts. There are no stoichiometry requirements, and equilibrium limitations are usually unimportant so that quite long chains are formed 7iv > 500 is typical of addition polymers. 

Metal complexes bound to a polymer support most frequently induce ionic polymerization of olefins, dienes and acetylenes, and less commonly radical polymerization of vinyl-type monomers, acting at all reaction stages initiation, chain propagation and termination. Active sites for the addition of monomer molecules to the growing polymer chain can in many cases be regenerated yielding new polymer chains (catalysis via a polymer chain). 

Metal-containing polymers are also applied to the catalysis of other processes such as polymerization and copolymerization of butadiene and isoprene (see, e.g., ref. (64)), oopolymerization of diene and olefin monomers and polymerization conversions of acetylene-type monomers (65). Such investigations are likely to be oriented both theoretically and practically. Metallopolymers can be used as advantage in some other catalytic processes (54), among them hydrogenation of imsaturated carpounds, oxidative conversions of hydrocarbons, in hydroformylation, polycondensation and other processes, etc. (Table 4). Catalysis of almost all reactions obeys the same or similar principles as in the case of polymerization. The position of metallopolymers in catalysis and their links with traditional catalysts can be illustrated as follows ... 

Polymer Chain Growth. The essential characteristic of Ziegler-Natta catalysis is the polymerization of an olefin or diene using a combination of a transition-metal compound and a base-metal alkyl cocatalyst, normally an aluminum alkyl. The function of the cocatalyst is to alkylate the transition metal, generating a transition-metal-carbon bond. It is also essential that the active center contains a coordination vacancy. Chain propagation takes place via the Cossee-Arlman mechanism (23), in which coordination of the olefin at the vacant coordination site is followed by chain migratory insertion into the metal-carbon bond, as illustrated in Figure 1. 

A high-throughput colorimetric assay was applied to identify catalysts by combining metals (Pd, Rh, Ru, Ir) and various phosphines for the hydroamination of dienes.217 Combinatorial catalysis was successfully used to find active catalysts in the Ru-catalyzed ring-closing metathesis reaction218 and the olefin polymerization by Ni and Pd.219... 

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