Polymers, organometallic synthesis

Boron-containing, Non-oxide Ceramics from Organometallic Polymers Synthesis, Thermolysis and the Influence of Boron on Materials Thermal Stability... 

Singler, R. E., Sennett, M. S., and Willingham, R. A., Phos-phazene polymers Synthesis, structure, and properties, in Inorganic and Organometallic Polymers (M. Zeldin, K. J. Wynne,... 

Organometallic polymer precursors offer the potential to manufacture shaped forms of advanced ceramic materials using low temperature processing. Polysilazanes, compounds containing Si-N bonds in the polymer backbone, can be used as precursors to silicon nitride containing ceramic materials. This chapter provides an overview of the general synthetic approaches to polysilazanes with particular emphasis on the synthesis of preceramic polysilazanes. 

One previous synthesis of ferrocene-containing condensation polymers via interfacial methods at room temperature has been reported by Knobloch and Rauscher, who formed low molecular weight polyamides and polyesters by reacting l,l -bis(chloro-formyl)ferrocene with various diamines and diols. Further, Carraher and co-workers have utilized interfacial techniques in the formation of other types of organometallic polymers. 

A large variety of organometallic compounds, e.g., metal alkoxides and metal carboxylates, has been studied as initiators or catalysts in order to achieve effective polymer synthesis [35]. Many reactions catalyzed by metal complexes are highly specific and, by careful selection of metal and ligands, reactions can be generated to form a desired polymer structure [36, 37]. The covalent metal alkoxides with freep or d orbitals react as coordination initiators and not as anionic or cationic inititors [38]. Fig. 1 summarizes some of the most frequently used initiators and catalysts. 

Silicon carbides are generally synthesized by the pyrolysis of precursors, prepared by liquid phase methods. One possible way for precursor synthesis is the addition of carbon black or sucrose, to a gelling silica.8 In this method, the carbon is introduced from an external source. A more intimate contact between the carbon and silicon in the precursor is assured with the use of organometallic polymer precursors. The use of silane polymers for silicon carbide production was initiated by Yajima.9,10 Polymers having a -[Si-C]- backbone are crosslinked and pyrolysed to yield SiC." In the initial work, dimethyldichlorosilane was used as a starting monomer, which was subjected to a sodium catalyzed polymerization (reaction (C)). 

Scheme 7 Synthesis of hyperbranched organometallic polymer from AB2-type monomer...

There has been considerable interest in the synthesis of polymers such as structure (6) in which aromatic rings and metal atoms alternate, due to the possibility of building extended electron-delocalized organometallic polymer chains. However, such a multiple decker polymer has not yet been synthesized, and only a few triple decker-sandwich compounds such as tris( 5-cyclopentadienyl)dinickel cation and tris-(cyclooctatetraene)dititanium dianion have been reported10. ... 

As discussed above in the mechanism of the alkene dimerization reaction, the polymerization of simple alkenes proceeds by the basic metathesis mechanism. Since polymers that are prepared from complex monomers require homogeneous catalysts, much of the early organometallic catalyst development has had polymer synthesis as the driving force. Recently, developments in the synthesis of organometal-lic complexes that serve as well-defined catalysts for metathesis have opened many opportunities in the area of polymer synthesis. ... 

The expectation that organometallics containing ligands with conjugated and delocalized tt systems will provide useful applications for the synthesis of new polyunsaturated organic substrates or serve as precursors to organometallic polymers displaying electronic conductivity and nonlinear optical properties has stimulated intense research efforts into their synthesis and properties. 

---