Silicon compounds polymers

The presence of carbon—fluorine bonds in organic polymers is known to characteristically impart polymer stabiUty and solvent resistance. The poly(fluorosibcones) are siloxane polymers with fluorinated organic substituents bonded to siUcon. Poly(fluorosibcones) have unique appHcations resulting from the combination provided by fluorine substitution into a siloxane polymer stmcture (see Silicon compounds, silicones). 

Silicones. Silicone fluids have a polymer-type stmcture except that the carbons in the backbone are replaced by silicon (see Silicon compounds, silicones). Dimethylpolysiloxane [9016-00-6] one of the widely used silicone fluids, has the stmcture... 

Sihcone products dominate the pressure-sensitive adhesive release paper market, but other materials such as Quilon (E.I. du Pont de Nemours Co., Inc.), a Werner-type chromium complex, stearato chromic chloride [12768-56-8] are also used. Various base papers are used, including polyethylene-coated kraft as well as polymer substrates such as polyethylene or polyester film. Sihcone coatings that cross-link to form a film and also bond to the cellulose are used in various forms, such as solvent and solventless dispersions and emulsions. Technical requirements for the coated papers include good release, no contamination of the adhesive being protected, no blocking in roUs, good solvent holdout with respect to adhesives appHed from solvent, and good thermal and dimensional stabiUty (see Silicon COMPOUNDS, silicones). 

The most significant difference between the alkoxysilanes and siUcones is the susceptibiUty of the Si—OR bond to hydrolysis (see Silicon compounds, silicones). The simple alkoxysilanes are often operationally viewed as Hquid sources of siUcon dioxide (see Silica). The hydrolysis reaction, which yields polymers of siUcic acid that can be dehydrated to siUcon dioxide, is of considerable commercial importance. The stoichiometry for hydrolysis for tetraethoxysilane is... 

Silicone Rubber. These polymers are based on chains of siUcon rather than carbon atoms, and owe thek temperature properties to thek unique stmcture. The most common types of siUcone mbbers are specifically and almost exclusively the polysdoxanes. The Si—O—Si bonds can rotate much more freely than the C—C bond, or even the C—O bond, so the siUcone chain is much more flexible and less affected by temperature (see Silicon COMPOUNDS, silicones). 

Before discussing the chemistry and technology of silicone polymers it is necessary to consider the methods of nomenclature of the silicon compounds relevant to this chapter. The terminology used will be that adopted by the International Union of Pure and Applied Chemistry. 

Tetravalent silicon is the only structural feature in all silicon sources in nature, e.g. the silicates and silica even elemental silicon exhibits tetravalency. Tetravalent silicon is considered to be an ana-logon to its group 14 homologue carbon and in fact there are a lot of similarities in the chemistry of both elements. Furthermore, silicon is tetravalent in all industrially used compounds, e.g. silanes, polymers, ceramics, and fumed silica. Also the reactions of subvalent and / or low coordinated silicon compounds normally lead back to tetravalent silicon species. It is therefore not surprising that more than 90% of the relevant literature deals with tetravalent silicon. The following examples illustrate why "ordinary" tetravalent silicon is still an attractive field for research activities Simple and small tetravalent silicon compounds - sometimes very difficult to synthesize - are used by theoreticians and preparative chemists as model compounds for a deeper insight into structural features and the study of the reactivity influenced by different substituents on the silicon center. As an example for industrial applications, the chemical vapor decomposition (CVD) of appropriate silicon precursors to produce thin ceramic coatings on various substrates may be mentioned. 

In the second, complementary, approach the polycondensation of silica polymer is followed by the formation of an organic network made by cross-linking reaction of monomers covalently bound to silicon compounds (Scheme 4.1) resulting in polymeric materials with outstanding protective abilities, including thermal, mechanical and corrosion resistance. 

For recent reviews of polysilane high polymers see West, R., J. Organometallic Chem. 1986, 300. 327 West, R. In The Chemistry of Organic Silicon Compounds Patai, S. Rappoport, Z. Eds. Wiley-Interscience New York, 1989 Vol. 2, Chapter 19, 1207. 

Drake, R. MacKinnon, I Taylor, R. Recent Advances in the Chemistry of Siloxane Polymers and Copolymers. In The Chemistry of Organic Silicon Compounds Rappoport, Z., Apeloig, Y., Eds. Wiley Chichester, 1998 Vol. 2, Part 3, Chapter 38, pp 2217-2244. 

The analogous silicon compounds are also unstable, but Lhe dimethylsilicone" that forms is a mixture of linear polymers (and cyclic products to be discussed in the next section) ... 

No section on hutcrocuicnution would he complete without a discussion of silicones. (K2SI0),.3-1 The term silicone wu.s coined by analogy to ketone under the mistaken belief that monomeric R Si=0 compounds could be isolated. Silicon compounds that are formally analogous to carbon compounds are found to have quite different structures. Thus carbon dioxide is a gaseous monomer, hut silicon dioxide is an infinite singly bonded polymer. In a similar manner, grm-diols are unstable relative to ketones ... 

SAN copolymers m [ACRYLONITRILE POLYMERS - SURVEY AND SAN (STYRENE-ACRYLONITRILE CO-POLYMERS)] (Vol 1) -silylatmg agents for [SILICON COMPOUNDS - SILYLATING AGENTS] (Vol 22)... 

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