Dimethyl silicone oils

The polymer has a waxy texture and is insoluble in a wide range of organic solvents. It does, however, form gel-like materials with solvents such as tetrahydrofuran, dioxane and chloroform. Not surprisingly in view of this, a mixture of a small amount of it and a large amount of a 1000 cs dimethyl-silicone oil forms a stiff, stable grease. When purified the polymer is a very pale blue. 

At shear stresses less than 4 kPa, Figure 6, two dimethyl silicone oils show Newtonian properties. Non-Newtonian, strong shear thinning behaviour is found in the range 4 kPa. Deviation from Newtonian characteristic Increases with the degree of polymerization (viscosity level). 

Figure 6 Two dimethyl silicone oils. The flow curves show Newtonian behaviour for stress below = 4 kPa. Strong shear thinning effects are seen at stresses above 4 kPA. Heating effects can be expected to be significant only above stresses of 100 kPa. Both materials remain liquid. Deviation from Newtonian properties Increases with degree of polymerization. L/D 54.2 and 5.33, 37.78 C, Pressure s.1 MPa. (11).

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,... 

Dimethyl-2-oxazoline is commercially available from Columbia Organic Chemicals, 912 Drake Street, Columbia, South Carolina, or may be prepared as follows. In a 250-ml., three-necked flask is placed 89.14 g. (1.0 mole) of 2-amino-2-methyl-l-propanol, and the flask is cooled in an ice bath. The amine is carefully neutralized with 52.3 g. (1.0 mole) of 90.6% formic acid over a 1-hour period. A magnetic stirring bar is added, the flask is fitted with a short path distillation head, and the reaction mixture is placed in a silicon oil bath which is rapidly heated to 220-250°. The azeotropic mixture of water and oxazoline distills over a period of 2-4 hours and is collected in an ioe-cooled flask containing ether. The aqueous layer is separated, saturated with sodium chloride, and extracted with three 50-ml. portions of ether. The combined ethereal extracts are dried over potassium carbonate, filtered to remove the drying agent, and the ether is removed at 35-40° at atmospheric pressure. The 4,4-dimethyl-2-oxazoline is collected as the temperature rises above 85°. The yield is 56.7-62.7 g. (57—63%) of a colorless mobile liquid, b.p. 99-100° (758 mm. Hg). 

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

The other major synthetic oils used in textile processing are the silicone oils, based on the polymers of dimethyl siloxane, (CHsjsSi—O—(—Si(CH3)2—O—) Si (CHsjs (55). 

Other studies reported in the literature involve the fractionation of a high molecular weight silicone oil, a poly(dimethyl)siloxane (Krukonis, 1983c). In the early 1980s, the material was being tested for an electronics application. 

Figure 17-2. Viscosity-temperature behavior of various types of synthetic lubricants. 1 White oil, VI 101. 2 4 -Undecy1-m-terphenyl. 3 Fluoroalkane. 4 -Di (chlorophenyl )pentane. 5 Polyphenyl ether. 6 Polyoxyalkylene glycol. 7 Di(2-ethylhexyl) sebacate. 8 Dimethyl silicone.

Figure 17-2 shows the influence of temperature on the viscosity of representative examples of synthetic fluids of various chemical types. Direct comparisons can be made when individual fluids have the same viscosity at a given temperature e.g. white oil and polyoxyalkylene glycol at 301 K (83 F). The viscosity of the glycol fluid at 372 K (210 F) is 6 Saybolt seconds higher than that of white oil, which is a significant difference that immediately shows the better viscosity behavior of the synthetic fluid. In similar fashion, u,u -di(chlorophenyl)pentane, di(2-ethylhexyl) sebacate and a dimethyl silicone all have a viscosity of 120 Saybolt seconds at 340 K (153 F) but at 372 K there is a spread of 15.7 Saybolt seconds in the viscosity behavior of these fluids. 

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