Metal atom aggregation process, initial

The free or polymer-bound bis(arene)metal complex can also react with metal atoms. Francis et al. (44) first published evidence that the siloxane-bound ic-complexes are converted to dimers and higher nuclearity clusters by additional metal atoms. Their experiments were conducted on quiescent thin liquid films of polymer applied to the optical window of a cryotip (see above, Small Scale Syntheses). Low nuclearity polymer-encapsulated molecules of Tin, Vn, Crn and Mon (n = 2-5) were inferred from quantitative studies of the metal atom aggregation process. The initial reaction appears to occur as follows ... 

Application of bulky ligands that fill the space around the countercation metal atom in covalent initiators prevent the aggregation - initially by Inoue and co-workers " and then by Spassky and co-workers ° - resulted in new mechanistic implications. Inoue introduced a notion of immortal polymerization for the already known processes with reversible chain transfer (the use of this expression is discouraged by lUPAC ). Polymerizations initiated with bulky chiral Schiff base Al alkoxides revealed a possibility of the stereodective polyester synthesis starting from the chiral cydic ester... 

In this coimection, a cryochemical solid-phase synthesis of metal-polymer systems is of special importance. As a result of such a synthesis, metal clusters and organometallic assemblies formed at low temperatures are buried in a polymer environment, which offers possibilities to stabilize and study these products over a large temperature range. This method was first offered and described in reference 10. The thermal rearrangement of the initial low-temperature system is governed by relaxation processes in polymer matrix. In particular, the aggregation of metal atom clusters to form metal nanocrystals in cryochemically produced metal-polymer systems yields new nanocomposite materials with valuable properties. The study of the mechanism of cluster aggregation, which depends on the characteristics of the polymer matrix, will allow the nanocomposite structure to proceed in the needed direction. Thus, it becomes possible to determine the methods of cryochemical synthesis of metal-polymer materials with predetermined properties. 

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