Insertion Polymerizations

The term coordination compiex polymerization was used for some time to embrace many systems that could give some control over the stereochemistry of the product. However, insertion polymerization is a more general description of polymerizations that include a hindered propagation site. 

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There appear to be two fundamental reasons for the absence of truly efficient transition metal-based insertion polymerization catalysts for the copolymerization of acrylate monomers with ethylene or other olefins. The first reason is that, following insertion, the ester group of the acrylate coordinates to the metal as shown by... 

The polymerization of conjugated dienes with transition metal catalytic systems is an insertion polymerization, as is that of monoalkenes with the same systems. Moreover, it is nearly generally accepted that for diene polymerization the monomer insertion reaction occurs in the same two steps established for olefin polymerization by transition metal catalytic systems (i) coordination of the monomer to the metal and (ii) monomer insertion into a metal-carbon bond. However, polymerization of dienes presents several peculiar aspects mainly related to the nature of the bond between the transition metal of the catalytic system and the growing chain, which is of o type for the monoalkene polymerizations, while it is of the allylic type in the conjugated diene polymerizations.174-183... 

The iso- and syndiotactic isomerism in the insertion polymerization of dienes (for 1,2 polymerization of generic dienes and for cis-1,4 polymerization of 4-monosubstituted or of 1,4-disubstituted monomers) would be determined, according to the polymerization scheme proposed by Porri and co-workers,181 182 by the relative orientations of the two ligands (diene monomer and allyl terminal of the growing chain) in the preinsertion catalytic intermediates. 

Two examples where actin polymerization is observed in eukaryotes are in the bacterial pathogens Listeria monocytogenes and Shigella flexneri. The motion that the eukaryote pathogens exhibit is the actin based motility in the cytoplasm of their host. Actin polymerization is known to occur via an insertion polymerization mechanism. The movement is a result of site-directed tread-milling of the actin filaments. This type of movement is classified as a propulsive type motion. The driving force for actin pol)unerization as well as the next motor is the conversion of adenosine triphosphate (ATP) to adenosine diphosphate (ADP). ... 

Depending on the nature of the active center, chain-growth reactions are subdivided into radicalic, ionic (anionic, cationic), or transition-metal mediated (coordinative, insertion) polymerizations. Accordingly, they can be induced by different initiators or catalysts. Whether a monomer polymerizes via any of these chain-growth reactions - radical, ionic, coordinative - depends on its con-... 

High magnetic fields and in particular C-NMR spectroscopy allow the analysis of even longer configurational sequences (tetrads up to nonads). This proved to be important in particular for the analysis of polyolefins like polypropylene or cycloolefin copolymers (COC). These polymers are available via transition-metal mediated (Ziegler-Natta, metallocene) insertion polymerizations, and the configurational analysis provides deep insight into the respective polymerization mechanisms as well as into the structure-property relationships. 

R. Grubbs, C. Bielawski, and D. Benitez, Synthesis of macrocyclic polymers by ring insertion polymerization of cyclic olefin monomers, US Patent 6946533, assigned to California Institute of Technology (Pasadena, CA), September 20,2005. 

When the transfer reaction competes successfully with further insertion, as in the case of nickel, dimerization becomes the dominant transformation. When metal hydride elimination, in turn, is slow relative to insertion, polymeric macromolecules are formed. Ligand modification, the oxidation state of the metal, and reaction conditions affect the probability of the two reactions. Since nickel hydride, like other metal hydrides, catalyzes double-bond migration, isomeric alkenes are usually isolated. 

This characteristic behaviour is comparable with anionic insertion polymerization rather than with radical polymerization. 

The chemistry of polymerization of the oxetanes is much the same as for THF polymerization. The ring-opening polymerization of oxetanes is primarily accomplished by cationic polymerization methods (283,313—318), but because of the added ring strain, other polymerization techniques, eg, insertion polymerization (319), anionic polymerization (320), and free-radical ring-opening polymerization (321), have been successful with certain special oxetanes. 

Pino, P., Giannini, U. and Porri, L., Insertion Polymerization , in Encyclopedia of Polymer Science and Engineering, Wiley-Interscience, John Wiley Sons, New York, 1987, Vol. 8, pp. 147-220. 

Paul, M-A., Alexandre, M., Degee, P., Calberg, C., Jerome, R., and Dubois, P. Exfoliated polylactide/clay nanocomposites by In-Situ coordination-insertion polymerization, Macromol. Rapid Commun. (2003), 24, 561-566. 

In presence of dienes (Scheme 1), heterodienes, and heterotrienes (Scheme 2) rapid cycloadditions take place which prevent other reaction modes of the silylenes (insertions, polymerization, or HX-elimination-polymerization). Although a concerted [l+4]-cycloaddition is symmetry-allowed a stepwise mechanism (Scheme 3) via a three-membered intermediate is prefered or at least partly be competing to account for the formation of double-bond isomers. Ususally the formal [4+l]-cycloadducts (allylsilane-type) are the main products while the isomers with vinylsilane-units are side-products (< 30 %). Exceptions are... 

As was shown earlier with the Suzuki coupling reactions, organopalladium intermediates can show good stability to water and other protic sources. This stability has been exploited in the synthesis of polyacetylene under air- and moisture-stable conditions. It was found that simple palladium(II) salts (PdCl2, Pd(CH3C02)2, etc.) can be used to initiate the 1,2-insertion polymerization of strained cyclic alkenes in water (eq. (8)) [31]. Once formed, poly-8 can be converted to polyacetylene through a retro-Diels-Alder reaction. 

In summary, this pioneering work clearly demonstrated the possibility of aqueous catalytic insertion polymerization of acyclic and cyclic olefins, as well as aqueous ROMP. On the other hand, metal salts without any additional ligands to control the properties of the metal centers were utilized, and activation to the active species was probably also relatively ineffective in most cases. Consequently, catalyst efficiencies were moderate at best. Most of the polymerizations also afforded low molecular weight materials, or employed rather special monomers. The possibility of polymer latex synthesis appears not to have received much attention, although free-radical emulsion polymerization of styrene and butadiene was already a large-scale process at the time. 

Recent Progresses in Catalytic Insertion Polymerization of Olefins... 

Since the aforementioned investigations, significant advances in aqueous catalytic insertion polymerization have only been made over the past decade. Alternating copolymerization of olefins with carbon monoxide, polymerization of ethylene and 1-olefins, and polymerizations of norbomenes and of butadiene have been studied. 

Catalytic Olefin and Alkyne Polymerization in Aqueous Systems 249 7.2.2.3 Miscellaneous Insertion Polymerizations... 

The coordination of the functionalities that may be present either in the monomer or in the growing polymer chain to the metal center is one key impediment in the development of new transition metal-based catalysts for the insertion polymerization of polar monomers. On the other hand, rapid -halide abstraction has prevented metal-catalyzed polymerization of vinyl halides. Several examples are discussed to illustrate these problems. 

A final illustration of the effect of coordinating functionalities on the polymerization of olefins by cationic metal complexes involves norbornene derivatives. The species, [Pd(PR3)(Me)]+, generated in situ by halide abstraction from [Pd(PR3)(Me)(Cl)]2, is an extremely active catalyst for the insertion polymerization of norbornene with a rate exceeding of 1000 tons norbornene/mol Pd hour at... 

Keywords Macromolecular stereochemistry. Main-chain chiral polymer, Atropisomeric polymer, Kinetic resolution. Anionic polymerization. Cationic polymerization. Insertion polymerization... 

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