Molecular weight metal coordination polymers

Examples of the pendant-type polymer-metal complexes represented by Schemes 4 and 5 are shown in Table 2. They are obtained by the reaction in Scheme 8 a polymer ligand is made to coordinate to a vacant site of a previously prepared, stable, low-molecular-weight metal complex. The structure and hence the functions of the metal complex are hardly changed by attachment to the polymer ligand. The metal complexes attached to the polymer ligands 1 to 8 are the classic cobaltic... 

Much more research has been carried out with polymers in which the coordinated metal atom is part of the chain backbone. Typically, the metal atoms are copper, nickel, and cobalt. Oxygen atoms or carbon atoms adjacent to the metal atom provide the electrons required for the coordinate bond.30 Polymers of this type are often rather intractable, for a variety of reasons. Specifically, insolubility can be a problem for species with moderate molecular weights. Also, coordination between chains can cause aggregation, and ligand-exchange reactions with small molecules such as solvents can cause chain scission. However, in some favorable cases, the intramolecular coordination is sufficiently strong for the polymer to be processed by the usual techniques such as spinning into fibers or extrusion into films.30... 

As a result of the particularities of the MAO activation method noticed so far, it has been concluded that, besides chain back-skip, a different mechanism occurs when using this cocatalyst. One possible explanation might be a reversible chain transfer reaction between the cocatalyst and the active species. As a result of the intrinsic chirality at the metal center, the catalytic system consists of two enantiomers (S and/ . Scheme 9.3). Under different polymerization conditions (i.e., different Al/Zr ratios), the coordination and insertion of the monomer can take place at the metal center of either of the two enantiomers. At higher Al/Zr ratios, a unidirectional transfer of polymer chains from Zr (enantiomer / , for example) to aluminum can be suggested, because reduced molecular weights of the polymer products have been found. Relocation of the chain from aluminum to the other enantiomer of the Ci-symmetric catalyst species (enantiomer 5, Scheme 9.3) and then back... 

A wide variety of polymer/clay nanocomposites can be synthesized by in situ coordinadmi polymerization methods, which gives the advantage of controlled molecular weight of the polymer nanocomposite. In the case of late transition metal-based coordination polymerization, the process is tolerant to the polar groups or to a little moisture in the clay or catalytic system. This moisture sensitivity can also be overcomed by treating the excess MAO or by in situ formation of MAO using TEA, TMA, or TIBA on the surface of clay, clay-MgCl2, or clay-silica hybrid material. 

The history of coordination polymers is much harder to define clearly and dates back at least to the 1930s. Stone and Graham reported some of the earliest examples of metal-coordination polymers. However, the insolubility of the products and their lack of molecular weight (MW) definition and characterization plagued early attempts to apply known coordination chemistry to polymer synthesis. One of the initial linear coordination polymers, silver cyanide (3), was reported in 1935 by West. ... 

The dehydrogenative coupling of silanes does not stop at the stage of disilanes in the coordination sphere of early transition metals like Zr and Hf, but chain polymers of low molecular weight are formed. As reactive intermediates in this reaction, silylene complexes are also assumed. However, alternative mechanisms have been discussed (sect. 2.5.4). 

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