Dimethylpolysiloxanes

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... 

Other U.S. regulatory clearances for sorbic acid allow its use as an antimicotic in the manufacture of food packaging materials (159), as a pesticide adjuvant when appHed to growing crops (160), and with methylceUulose and dimethylpolysiloxane as an antifoaming agent (161). 

Figure 29.2. Viscosity-temperature curves for four commercial dimethylpolysiloxane fluids and for liquid paraffin. The numbers 1000, 300, 100 and 40 indicate the viscosities in centistokes at 38°C.

Therapeutic Function Antiflatulent Chemical Name Dimethylpolysiloxane Common Name Simethicone... 

For routine separations, there are about a dozen useful phases for capillary columns. The best general-purpose columns are the dimethylpolysiloxane (DB-1 or equivalent) and the 5% phenyl, 95% dimethylpolysiloxane (DB-5 or equivalent). These relatively nonpolar columns are recommended because they provide adequate resolution and are less prone to bleed than the more polar phases. If a DB-1, DB-5, or equivalent capillary column does not give the necessary resolution, try a more polar phase such as DB-23, CP-Sil88, or Carbowax 20M, providing the maximum operating temperature of the column is high enough for the sample of interest. See Appendix 3 for fused silica capillary columns from various suppliers. 

The standard materials used are nonionic dimethylpolysiloxanes, and these are available in ranges of controlled MWs with viscosities varying from 10,000 to 50,000 centistokes (cs). These silicones follow the general formula ... 

Fused-silica megabore column, DB-1, 15 m x 0.53-mm i.d., 1.5- im fllm thickness, 100% dimethylpolysiloxane... 

Fused silica capillary columns of various internal bores and of lengths in the range 25 to 50 m are mainly employed for analytical separations. A variety of polar and non-polar column types are available including those open tubular types with simple wall coatings (WCOT), those with coatings dispersed on porous solid-supports to increase adsorbent surface area (SCOT) and porous layer open tubular (PLOT) columns. Important stationary phases include polyethylene glycol, dimethylpolysiloxane and different siloxane copolymers. Various sample introduction procedures are employed including ... 

Intensive investigations have shown that specific silica-silicone mixtures or paraffin oil systems are considerably more universal in their applicability and that their effectiveness is independent of both water hardness and the nature of the surfactant-builder system employed [31-33]. Therefore, most heavy-duty detergents in Europe have silicone oil and/or paraffins as foam depressors. Soap has almost lost its importance as a foam regulator. Silica-silicone systems, frequently called silicone antifoams, are usually commercially available as concentrated powders. The key silicone oils used for antifoams are dimethylpolysiloxanes. 

Neal 2691 dissolved dimethylpolysiloxanes in MIBK, and analyzed the solution for silicon. Inorganic silicons commonly found in food and 1 % cottonseed oil did not interfere. Jordan 2731 extracted lead from food into xylene rather... 

Materials and instrumentation. Experiments were performed using a special home-made cell coupled to a dual current supply with a maximum output of 10 V/40 mA. A detailed technical description of this system is published elsewhere (10). H NMR spectra were recorded on a Varian Mercury vx300 instrument at 25 °C. GC analysis was performed on an Interscience GC-8000 gas chromatograph with a 100% dimethylpolysiloxane capillary column (DB-1, 30 m x 0.325 mm). GC conditions isotherm at 105 "C (2 min) ramp at 30 °C min to 280 °C isotherm at 280 °C (5 min). Pentadecane was used as internal standard. The ionic liquid [omim] [BF4] was prepared following a published procedure and dried prior to use (8). All other chemicals were purchased from commercial sources (> 98% pure). 

Elastomer Natural rubber Halobutyl rubber Dimethylpolysiloxane polymer EPDM... 

More recent efforts in analytical improvements have focused on maximizing the separation of PCN congeners by capillary gas chromatography, jarnberg et al. investigated capillary GC columns of varying polarity and structural selectivity, finding that the 5% phenyl-dimethylpolysiloxane sta-... 

Owing to the high thermal and long-term stability, amide phases bonded to polysiloxane are regarded as sensitive materials for the sensoric approach to enantiomeric separation. An important factor for the resolution of the stationary material is the number of dimethylpolysiloxane units between the chiral moieties. More than 200 different amide phases have been synthesised and applied for the discrimination of amino acids, lactate esters and many other substances [10]. 

Structural Formula Dimethylpolysiloxane Chemical Abstracts Registry No. 8050-81-5... 

Enantiomer separation of various compounds such as barbituric acids, benzoin, MTH-proline, glutethimide, a-methyl-oc-phenyl-succinimide, y-phenyl-y-butyrolac-tone, methyl-mandelate, l-(2-naphthyl)ethanol, mecoprop methyl, diclofop methyl and fenoxaprop methyl by pressure supported CEC on a permethyl-P-cyclodextrin modified stationary phase was described by Wistuba and Schurig [42-44]. Three different separation beds were used (i) permethyl-P-cyclodextrin was covalently attached via a thioether to silica (Chira-Dex-silica) [42], permethyl-P-cyclodextrin was linked to a dimethylpolysiloxane and thermally immobilized (ii) on silica (Chirasil-Dex-silica) [43] or (iii) on a silica monolith (Chirasil-Dex-monolith) [44], respectively. 

Maki, H., Horiguchi, Y., Suga, T. and Komori, S. (1970) Syntheses and properties of organometallic surfactants VII. Cationic surfactants containing dimethylpolysiloxane. Yukagaku, 19, 1029-33. 

Tanaka, T. Heats of combustion and formation of lower members of methoxy end-blocked dimethylpolysiloxanes. J. inorg. nuclear Chem. 13, 225-230 (1960). 

Procedure (See Chromatography, Appendix IIA) Use a gas chromatograph equipped with a split injector and an electron-capture detector and fitted with a 50-m x 0.2-mm (id), fused-silica column (Carbowax 20M, or equivalent) coated with dimethylpolysiloxane, or equivalent. Use nitrogen as the carrier gas at a flow rate of 8 mL/min. Before use, precondition the column by heating it at 200° and the detector at 300° for 24 h. Set the injector temperature at 250° and the electron-capture detector at 300°, and program the column temperature as follows Maintain for 10 min at 115°, raise rapidly at 307 min to 200°, and maintain at 200° for 12 min. 

Dimethylpolysiloxane occurs as a clear, colorless, viscous liquid. It is a mixture of fully methylated linear siloxane polymers containing repeating units of the formula (CH3)2SiO that are terminated with trimethylsiloxy end-blocking units of the formula (CH3)3SiO—. It is soluble in most aliphatic and aromatic hydrocarbon solvents, but it is insoluble in water. Note Dimethylpolysiloxane is frequently used in commerce as such, or as a liquid containing silica (usually 4% to 5%), which must be removed by high-speed... 

Identification The infrared absorption spectrum of a neat dispersion of the sample between two sodium chloride plates exhibits relative maxima at the same wavelengths as those of a similar preparation of USP Dimethylpolysiloxane Reference Standard. 

Viscosity Determine as directed under Viscosity of Dimethylpolysiloxane, Appendix IIB. 

Viscosity of Dimethylpolysiloxane. .. 848 Method I Thorium Nitrate Colorimetric ... 

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