Dimeticone BP Grade

Ph Eur --- 9006-75-9
Action and use: Antifoaming agent; water repellent. When dimethicone is demanded, Dimeticone shall be supplied.

DEFINITION
Poly(dimethylsiloxane) obtained by hydrolysis and polycondensation of dichlorodimethylsilane and chlorotrimethylsilane. Different grades of dimeticone exist which are distinguished by a number indicating the nominal kinematic viscosity placed after the name.
Their degree of polymerisation (n = 20 to 400) is such that their kinematic viscosities are nominally between 20 mm2·s-1 and 1300 mm2·s-1.
Dimeticones with a nominal viscosity of 50 mm2·s-1 or lower are intended for external use only.

CHARACTERS
Appearance: Clear, colourless liquid of various viscosities.
Solubility: Practically insoluble in water, very slightly soluble or practically insoluble in anhydrous ethanol, miscible with ethyl acetate, with methyl ethyl ketone and with phenylmethane.

IDENTIFICATION
A. It is identified by its kinematic viscosity at 25C (see Tests).
B. Infrared absorption spectrophotometry.
C. Heat 0.5 g in a test-tube over a small flame until white fumes begin to appear. Invert the tube over a 2nd tube containing 1 ml of a 1 g/l solution of chromotropic acid sodium salt in sulphuric acid so that the fumes reach the solution. Shake the 2nd tube for about 10 s and heat on a water-bath for 5 min. The solution is violet.
D. In a platinum crucible, prepare the sulphated ash using 50 mg. The residue is a white powder that gives the reaction of silicates.

TESTS
Acidity: To 2.0 g add 25 ml of a mixture of equal volumes of anhydrous ethanol and ether, previously neutralised to 0.2 ml of bromothymol blue solution and shake. Not more than 0.15 ml of 0.01 M sodium hydroxide is required to change the colour of the solution to blue.
Viscosity: 90 per cent to 110 per cent of the nominal kinematic viscosity stated on the label, determined at 25C.
Mineral oils: Place 2 g in a test-tube and examine in ultraviolet light at 365 nm. The fluorescence is not more intense than that of a solution containing 0.1 ppm of quinine sulphate in 0.005 M sulphuric acid examined in the same conditions.
Phenylated compounds: Dissolve 5.0 g with shaking in 10 ml of cyclohexane. At wavelengths from 250 nm to 270 nm, the absorbance of the solution is not greater than 0.2.
Heavy metals: Maximum 5 ppm.
Volatile matter: Maximum 0.3 per cent, for dimeticones with a nominal viscosity greater than 50 mm2·s-1, determined on 1.00 g by heating in an oven at 150 °C for 2 h. Carry out the test using a dish 60 mm in diameter and 10 mm deep.

LABELLING
The label states:
-the nominal kinematic viscosity by a number placed after the name of the product,
-where applicable, that the product is intended for external use.

Dimethicone USP Grade

-(Trimethylsilyl)- -methylpoly[oxy(dimethylsilylene)] [9006-65-9].
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.

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: within the limits specified in the accompanying table.
Viscosity: Determine the viscosity of Dimethicone having a nominal viscosity of less than 1000 centistokes at 25 ± 0.1 , using a capillary viscosimeter. Determine the viscosity of Dimethicone having a nominal viscosity of 1000 centistokes or greater at 25 ± 0.1 , using a rotational viscosimeter. The viscosity is within the limits specified in the accompanying table.
Refractive index: within the limits specified in the accompanying table.
Acidity: Dissolve 15.0 g in a mixture of 15 mL of phenylmethane and 15 mL of butyl alcohol, previously neutralized to bromophenol blue 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 150C for 30 minutes, and allow to cool to room temperature. Tare the vessel, transfer to it about 1 g of Dimethicone, accurately weighed, heat at 150C in a circulating air oven for 2 hours, and allow to come to room temperature in a desiccator before weighing: it loses not more than the maximum percentage of its weight specified in the accompanying table.
Heavy metals: To pass the test (5 microgm per g).
Bacterial endotoxins: To pass the test: equivalent to not more than 10 Endotoxin Units per mL of the Dimethicone taken.

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Nominal Viscosity	viscosity (centistokes)	Specific gravity	Refractive index	Loss on heating
(centistokes)	Min. to Max.	Min. to Max.	Min. to Max.	Max.
20	18 to 22	0.946 to 0.954	1.3980 to 1.4020	20.0
50	47.5 to 52.5	0.955 to 0.965	1.4005 to 1.4045	2.0
100	95 to 105	0.962 to 0.970	1.4005 to 1.4045	0.3
200	190 to 220	0.964 to 0.972	1.4013 to 1.4053	0.3
350	332.5 to 367.5	0.965 to 0.973	1.4013 to 1.4053	0.3
500	475 to 525	0.967 to 0.975	1.4013 to 1.4053	0.3
1000	950 to 1050	0.967 to 0.975	1.4013 to 1.4053	0.3
12,500	11,875 to 13,125	--	1.4015 to 1.4055	2.0
30,000	27,000 to 33,000	0.969 to 0.977	1.4010 to 1.4100	2.0