Siloxanes, silicon compounds

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. Polydimethylsiloxanes, polydiphenylsiloxanes, and polymethylphenylsHoxanes are generally called siUcones (see Silicon COMPOUNDS, silicones). With a repeating unit of alternating siUcon-oxygen, the siloxane chemical backbone stmcture, siUcone possesses excellent thermal stabiUty and flexibility that are superior to most other materials. Polydimethjisiloxane provides a very low glass-transition temperature T material but is suitable for use... 

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. 

In the above mentioned series, surprisingly the stability of the compounds in air increases. The silicon compounds decompose instantaneously into phosphane and siloxane the lead compounds in contrast, however, react only in the course of some days. The systematic changes in the i.r. spectra are also interesting. The M-P and M-C vibrations show the expected shift with atomic mass, whereas the vibrations of the P7-cages remain completely unaffected by the substitution (2). 

Radiation methods -of cyclic siloxanes [SILICON COMPOUNDS - SILICONES] (Vol 22) -dye wastewater treatment [DYES, ENVIRONMENTAL CHEMISTRY] (Vol 8)... 

This reaction made numerous silicon compounds available and even today is still of great importance. Kipping expected to find an analogy between silicon and carbon compounds, but his later papers reveal his disappointment in the lack of versatility and limited reactivity of silicon compounds. Kipping was rather pessimistic about the further development of organosilicon chemistry, being so much influenced by ideas of carbon chemistry that he underestimated the importance of the formation of the siloxanes from the silicon halides, as now evidenced in the industrial applications of organosilicon compounds. 

Silicon halides (especially the readily available chlorides) are probably the most synthetically useful and versatile monomeric inorganic silicon compounds. They may readily be reduced to hydrides, hydrolyzed to silanols (and subsequently to siloxanes), treated with other protic species such as alcohols, carboxylic acids, amines, and thiols to give SiA)R, Si-0C(0)R, Si NR2, and Si SR species respectively, used to make sUyl pseudohalogen derivatives by treatment with silver or alkali metal salts, for example, treated with sodium... 

The wide range of silicon compounds that are readily hydrolyzed means that the siloxane H3SiOSiH3 is formed (probably via H3 SiOH) in numerous reactions (Scheme 35). Similarly, hydrolysis of halodisilanes tends to give siloxane rather than silanol products (Scheme 36). ... 

An investigation into the effect of certain organic silicon compounds on the properties of aminoplasts was made in Ref. [7]. It was shown that the modification of aminoplasts with siloxanes makes it possible to improve their stren h and performance indices, such as the collapse strain in bending, thermal resistance, and to reduce water absorption. The maximum effect is obtained by the use of 1-1.5% hydroxyloxane as a modifying additive. 

E(Si - O) is deduced from the heats of formation of some linear polydimethyl siloxanes to be 117 kcal by Thompson 21 jje also obtains 104 kcal for (Si 0) in amorphous silica see Section iO.6.14). The reliability of bond energy terms in the prediction of heats of formation of organo-silicon compounds is doubtful the situation has been discussed by Thompson 21,... 

The properties and applications of commercially important hydride functional silanes, ie, compounds having a Si—H bond halosilanes, ie, compounds having a Si—X bond and oiganosianes, ie, compounds having a Si—C bond, are discussed herein. Compounds having Si—OSi bonds are called sioxanes or sflicones. Those having a Si—OR bond are called sflicon esters. Siloxanes and sflicon esters are discussed elsewhere in the En c/opedia (see Silicon COMPOUNDS, SILICON ESTERS SILICON COMPOUNDS, SILICONES). 

The MM2 force field has also been parameterized for silicon-containing molecules by Grigoras and Lane.i- The parameters were based on ab initio calculations and included new bond stretch, angle bend, torsional, and van der Waals parameters, which accurately reproduced the ab initio calculated properties of small silanes, polysilanes, and siloxanes. The same authors used this force field to study the structures of some biologically active compounds containing silicon. The siloxane 2,6-c/s-diphenylhexamethylcyclotetrasiloxane (9) has estrogenlike activity. Grigoras and Lane compared the distance between... 

T. C. Kendrick, B. Parbhoo, J. W. White, Siloxane polymers and copolymers in The Chemistry of Organic Silicon Compounds (Eds. S. Patai, Z. Rappaport), Wiley, 1989, p. 1347. 

Altering the molecular weight of the silicone compound affects the siloxane content, the mechanical properties, and the softening temperatures. 

Industrially produced organo-silicon compounds include monomeric low molecular compounds, almost exclusively belonging to the class of silanes, and oligomers and polymeric compounds including oligomeric silanes, polysilanes, oligomeric silazanes, polysilazanes and particularly oligomeric siloxanes and polysiloxanes (silicones). 

The discussion following will deal mainly with the important equilibrations and polymerizations of cyclic siloxanes. For further information concerning these methods and for excellent discussions of other types of siloxane polymerizations, the reader is referred to Voronkov (O, Noll O), and Meals (10). In addition, Noll (7, Eaborn (11), and Arkles and Peterson ( 1 2) offer reviews of the general chemistry of silicon compounds. 

The chemical shifts of groups bonded to the oxygen atom of the silicon ethers (siloxanes) are described with the other ether oxygen compounds. 

The preparation1 and properties2 of a great many organo-silicon compounds have been described. However, a relatively small amount of work has been done in the field of silazane chemistry, i.e., the chemistry of compounds which contain at least one silicon-nitrogen bond.3-8 In general, this group of compounds has been found to be extremely sensitive to hydrolysis. The hydrolytic reaction forms the appropriate amine or ammonia and a silanol and/or a siloxane. 

Siloxanes represent another large class of silicon compounds for which 29Si-NMR data would be useful. The compound HMe2SiOSiMe2H was chosen as a representative siloxane with a more complex spin system due to the Si-H moieties. The proton coupled spectrum (Fig. 4) consists of a major doublet (J = 204 Hz), for which INEPT and DEPT parameters were set, and a minor septet of doublets. In the INEPT spectrum (Fig. 4a) the major doublet shows the expected INEPT intensities (+1 — 1), while the minor splittings show normal coupling intensities. A subtle but important distortion is present in the INEPT spectrum the expected septet of doublets... 

Hydrolysis in the silicones is usually just a special case of the reaction with organic halides. The most important reaction is the preparation of siloxanes by the hydrolysis of chlorosilanes and the subsequent condensation to form the commercially important polysiloxanes (see Chap. 15). Diethyl silane diol, (CjHs)2Si(OH)s, and the corresponding di-n-propyl and di-n-butyl diols have been made by hydrolyzing the dichlorosilanes. The trimethyl and triethyl silicon hydroxides have been prepared by the hydrolysis of complex organic silicon compounds containing the aceto and the amino group, respectively. ... 

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