Dimethicone
» Dimethicone is a mixture of fully methylated linear siloxane polymers containing repeating units of the formula:
[–(CH3)2SiO–]n
stabilized with trimethylsiloxy end-blocking units of the formula:
[(CH3)3SiO–]
wherein n has an average value such that the corresponding nominal viscosity is in a discrete range between 20 and 30,000 centistokes. It contains not less than 97.0 percent and not more than 103.0 percent of polydimethylsiloxane ([–(CH3)2SiO–]n).
The requirements for viscosity, specific gravity, refractive index, and loss on heating differ for the several types of Dimethicone, as set forth in the accompanying table.
Packaging and storage—
Preserve in tight containers.
Labeling—
Label it to indicate its nominal viscosity value. Dimethicone intended for use in coating containers that come in contact with articles for parenteral use is so labeled.
Identification—
Its IR absorption spectrum, obtained as directed in the Assay, exhibits maxima only at the same wavelengths as that of USP Polydimethylsiloxane RS, obtained as directed in the Assay.
Specific gravity
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Viscosity
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Refractive index
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Acidity—
Dissolve 15.0 g in a mixture of 15 mL of toluene and 15 mL of butyl alcohol, previously neutralized to bromophenol blue TS, and titrate with 0.050 N alcoholic potassium hydroxide to a bromophenol blue endpoint: not more than 0.10 mL is required.
Loss on heating—
Preheat an open aluminum vessel (60 mm in diameter and 10 mm high) at 150
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Heavy metals—
Mix 1.0 g of Dimethicone with 10 mL of chloroform, and dilute with the same solvent to 20 mL. Add 1.0 mL of a freshly prepared 0.002% solution of dithizone in chloroform, 0.5 mL of water, and 0.5 mL of a mixture of 1 volume of ammonia TS and 9 volumes of a 0.2% solution of hydroxylamine hydrochloride. Concomitantly prepare a Standard solution as follows: to 20 mL of chloroform add 1.0 mL of a freshly prepared 0.002% solution of dithizone in chloroform, 0.5 mL of Standard Lead Solution (see Heavy Metals
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Bacterial endotoxins
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Assay—
Use an IR spectrophotometer with a resolution of 4 cm
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() 100(AU / AS)(DS / DU)
in which AU is the absorbance of the Dimethicone; AS is the absorbance of USP Polydimethylsiloxane RS; and DS and DU are the specific gravities of USP Polydimethylsiloxane RS and Dimethicone, respectively.
Auxiliary Information—
Please check for your question in the FAQs before contacting USP.
USP32–NF27 Page 1229
Pharmacopeial Forum: Volume No. 29(1) Page 142
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