Dimethyl-silicone

Silcones are important products of silicon. They may be prepared by hydrolyzing a silicon organic chloride, such as dimethyl silicon chloride. Hydrolysis and condensation of various substituted chlorosilanes can be used to produce a very great number of polymeric products, or silicones, ranging from liquids to hard, glasslike solids with many useful properties. 

Foam Control. Whereas some siUcones are known to be foam promoters, Dow Corning FS-1265 Fluid is a Hquid fluorosiUcone with effective antifoam properties. Petroleum industry appHcation of fluids and dispersions in gas—oil separators on offshore drilling platforms has been successful. Their use peaked in the early 1980s, coinciding with constrained cmde oil capacity and production. Diesel fuels are an excellent solvent for dimethyl silicones and render them ineffective as an antifoam. A new antifoam which does not require the use of added siUca is formulated from a fluorosiUcone copolymer. It has shown promise to antifoam (8) diesel fuel (see Defoamers). 

Silicone Fluids. Sihcone fluids are used in a wide variety of appHcations, including damping fluids, dielectric fluids, poHshes, cosmetic and personal care additives, textile finishes, hydraiflic fluids, paint additives, and heat-transfer oils. Polydimethylsiloxane oils are manufactured by the equihbrium polymerisation of cycHc or linear dimethyl silicone precursors. Trifunctional organosilane end groups, typically trimethylsilyl (M), are used, and the ratio of end group to chain units (D), ie, M/D, controls the ultimate average molecular weight and viscosity (112). Low viscosity fluids,... 

Fig. 4. Kinematic viscosity—temperature relationship of dimethyl silicone fluids.

The assay of ethyleneamines is usually done by gas chromatography. Compared to packed columns, in which severe tailing is often encountered due to the high polarity of the ethyleneamines, capillary columns provide better component separation and quantification. Typically, amines can be analyzed using fused siUca capillary columns with dimethyl silicones, substituted dimethyl silicones or PEG Compound 20 M as the stationary phase (150). 

Chlorine Dimethyl silicone (DMS) (single-backed) Buffered (pH 7) Fluorescein, 0.005% NaBr (0.31%) 0.013 ppm (8-hr exposure)... 

Silicone rubbers are normally cured with peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide and t-butyl perbenzoate being used for the dimethyl-silicones in quantities of 0.5-3%. These materials are stable in the compounds for several months at room temperature but will start to cure at about 70°C. 

Dimethyl Silicone Elastomers They are having linear polymers of very high Molecular weight within the range of 30,000-7,00,000. In order to prepare these polymers, dimethyl dichlorosilane is made to dissolve in ether and the solution is then mixed with excess of water. 

Gasoline analyses were performed by gas chromatography using a 50 m dimethyl silicon capillary column temperature programmed to 280°C. 

Gas chromatographic analysis (0.53-mm id x 10 m poly (dimethyl silicone) fused silica column, temperature programmed from 140°C to 220°C) indicates that this product is 98% pure, with <1% 3-methyl-1-phenyl-1,3-butadiene and 1-2% of a less volatile, unidentified component. The checkers could obtain a very pure product by normal vacuum distillation. They found the impurities to be higher boiling compounds. 

Silicones Dimethyl silicone, trialkyl and tetraalkyl silanes Lubricating oils distillation fermentation jam and wine making food processing... 

A study of the alkoxyl-alkoxyl group exchange (145) on the dimethyl-silicon moiety between dimethyldiethoxysilane and dimethyldi-iec-butoxy-silane, the latter prepared from optically active rec-butanol, showed that the optical activity was retained in the product... 

An equilibrium constant which is larger than the random value is observed for the exchange of methoxyl with methylthio groups. Similar values also have been found for the exchange of these substituents on the dimethyl-silicon moiety. 

Certain cerium and iron compounds, when properly incorporated by preoxidation, are excellent antioxidants for dimethyl silicone fluids (DMS) and methylphenylsilicone fluids (MPS). The useful life of these stabilized fluids depends on the temperature, on the concentration and dispersion of the redox metal moieties, and on the conditions of aeration—better aeration providing the longer useful life with inhibited DMS. A mechanism of stabilization by the redox metals has been proposed to account for the observed data. 

Another relatively nonpolar liquid, but one with a very high temperature limit, is a carborane silicone polymer called Dexsil, first synthesized by Olin Chemical in 1964 and now manufactured by Analabs and by a company bearing the Dexsil name. Its structure is shown in Figure 8.16. Three polymers are available that differ in the substitution on the methyl silicone backbone in a way similar to the silicones discussed above Dexsil 300 is dimethyl silicone, as shown in the figure Dexsil 400 is the methyl-phenyl analog and Dexsil 410 is the methyl-cyanopropyl analog. The temperature range over which they can be used is approximately 50 to 400°C. 

Livingston, R. L., and L. 0. Brockway The Molecular Structures of Dimethyl Silicon Dichloride, Methyl Silicon Trichloride and Trifluoro Silicon chloride. J. Amer. chem. Soc. 66, 94—98 (1944). 

---