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Dimethicone Excipient | Uses, Suppliers, and Specifications
Dimethicone (sometimes referred to as Poly(dimethylsiloxane or PDMS), is a synthetic polymeric organosilicon compound commonly known as silicone. In reality, Dimethicone is a group of related silicones that vary in molecular weight and physical properties. However, they all correspond to the general chemical formula (H3C)3[Si(CH3)2O]nSi(CH3)3, where n is the number of repeating monomer [SiO(CH3)2] units. Dimethicone is supplied as a clear, colourless thin or highly viscous liquid, that exhibits an oily feel.
Synonyms and Trade names: Dimethicone; Dimethyl siloxane, Dimeticone; Trimethylsiloxy-terminated; Dimethylsilicone Fluid; Dimethylsiloxane; Dow Corning® Q7-9120; Dupont® Liveo® Q7-9120; Poly(dimethylsiloxane); PDMS; ABIL®
Pharmacopoeial Compliance: USP-NF; Ph.Eur; B.P; J.P; IP
Uses and Applications: Antifoaming Agents, Emollients, Lubricants, and Water-Repelling Materials
Description
Dimethicone (also referred to as Poly(dimethylsiloxane), PDMS or Dimeticone), is a synthetic polymeric organosilicon substance that is widely known as silicone. It consists of a repeating chain of –Si–O– units, with methyl groups attached to the silicon atoms and corresponds to the general chemical formula (H3C)3[Si(CH3)2O]nSi(CH3)3, where n is the number of repeating monomer [SiO(CH3)2] units.
In the Ph.Eur, Dimethicone is defined as a polydimethylsiloxane made by hydrolysis and polycondensation of dichlorodimethylsilane and chlorotrimethylsilane. Depending on the degree of polymerization (n), Dimethicone is available in different grades (n = 20–400) and yields materials with viscosities approximately between 20 – 1300 cSt. Grades with a nominal viscosity of ≤50 cSt are authorised for external use only.
The USP-NF defines dimethicone as a mixed polymer consisting of fully methylated linear siloxane polymers made up of repeating residues corresponding to the formula [-CH3)3SiO-] balanced by trimethylsiloxy end-blocking units corresponding to the formula [CH3)3SiO-], where n has an average value such that the corresponding nominal viscosity is in a discrete range 20—30 000 cSt.
Chemical Structure & Identifiers
| Chemical Name | Dimethyl siloxane, trimethylsiloxy-terminated |
| CAS Registry Number | [9006-65-9], [63148-62-9] |
| Empirical Formula
Molecular Weight |
(C2H6OSi)n
n(162.378) |
| EC Number | 618-433-4 |
| UNII Code (FDA) | 92RU3N3Y10 |
Regulatory Status
Dimethicone is an approved excipient and is monographed in the PhEur and USP-NF. It is also accepted for use as a food additive in Europe (E900a). Dimethicone is included in the US FDA Inactive Ingredients Database (covering oral capsules and tablets, topical creams, emulsions, lotions, and transdermal preparations). Dimethicone is also approved for use in cosmetic formulations.
Physicochemical Properties
| Physical form | Liquid |
| Appearance | Clear, colourless oily liquid |
| Acid value | <0.01 |
| Density | 0.94—O.98 g/ml (25 oC) |
| Refractive index | n = 1.401—1.405 |
| Solubility | Practically insoluble in water, Glycerin, Propylene glycol, and Polyethylene glycol. Very slightly soluble in ethanol. Miscible with Ethyl acetate and mineral oil. Soluble in Isopropyl myristate |
| Surface tension (25 oC) | 20.5-21.2 mN/m |
| Viscosity | 20-1300 cSt (Higher viscosities available) |
Pharmacopeoeal Specifications
| USP-NF | Ph.Eur | |
| Name | Dimethicone | Dimeticone |
| Authorised use | Excipient and Aactive Pharmaceutical Ingredient | Excipient and Aactive Pharmaceutical Ingredient |
| Definition | specified | specified |
| Identification | specified | specified |
| Appearance | n/a | Clear, colourless liquid |
| Viscosity | specified | specified |
| Specific gravity | specified | n/a |
| Acidity | specified | specified |
| Mineral oils | n/a | specified |
| Phenylated compounds | n/a | ≤0.2 |
| Heavy metals | ≤5 µg/g | ≤5ppm |
| Volatile matter | n/a | ≤3.0% |
| Refractive index | specified | n/a |
| Loss on heating | specified | n/a |
| Assay | 97.0-103.0% | n/a |
| Endotoxins (for coating glass vials intended for parenteral uses) | specified | n/a |
| Labelling | specified | n/a |
Key: n/a Specification is not listed
*All claims with respect to conformity are subject to our Terms and Conditions. No express or implied warranty is made for specific properties or fitness for any particular application or purpose.
Applications in Pharmaceutical Formulations or Technology
Dimethicone is a versatile excipient that has many uses in pharmaceutical, cosmetic and food formulations, including:
• Antifoaming agents
• Emollients
• Lubricants
• Water-repelling materials
Within the cosmetic and pharmaceutical field, Dimethicone is used in topical oil-in-water and silicone-in-water type emulsions where it functions as an emollient, film former and substantivity agent. It is typically added at levels of between 0.5-5.0% for oil-in-water emulsions or 10-30% for creams, lotions and ointments. A major application of Dimethicone is in the area of topical medical products (barrier creams).
Dimethicone is used in these applications owing to its safe and well-known aesthetics that consumers appreciate. They are also appreciated for their ease of spreading, low tackiness, and a silkier, “elegant” and more lubricious feel than comparable formulations without Dimethicone.
Other uses of Dimethicone
- Film former/coating agent for glass vials (as a way of repelling water (hydrophobisation)
- Lubricant (personal and for preventing skin chaffing)
- Therapeutic (as Simethicone) in oral pharmaceutical products for the management of flatulence
Safety and Precautions
Dimethicone is a long-established raw material that is generally considered relatively nontoxic and non-irritant. It is authorised for use in topical and oral pharmaceutical products and is extensively added to personal care products. Dimethicone is also an approved food additive. However, it reportedly can cause irritation upon contact with mucous membranes (e.g eyes). When used in skin products, Dimethicone is non-comedogenic.
A tentative estimated ADI (acceptable daily intake) for Dimethicone as set by the World Health Organisation has been reported to be up to 1.5 mg/kg body-weight for Dimethicone with a relative molecular weight of 200-300 g/mol. Parenteral administration is harmful and causes chronic inflammation or even death.
Toxicology: LD50 (mouse, oral: >20g/kg
Stability and Storage Conditions
Dimethicones are stable excipients and generally resistant to thermal stress or chemical attack except for strong acids. The assigned shelf life is 24-36 months. The bulk material should be stored in an airtight container in a cool dry place, away from direct sunlight or moisture.
Constituted films of Dimethicone are suitable for heat sterilisation (2 hours at 160 oC). Autoclaving is not ideal as excess water may become trapped in the material turning it hazy. It is possible to sterile Dimethicone with gamma irradiation however this can cause polymer crosslinking, increasing the nominal viscosity of the material.
When handling bulk material, observe applicable SHEQ protocols appropriate to the prevailing circumstances and quantity of material being processed. Avoid naked flames as the material is combustible.
Sustainability and Environmental Impact
A sustainability assessment for Dimethicone has not been conducted.
Manufacturers & Suppliers
Additional Resources (Downloads)
References and Literature Used
[2] C. Séné, D. Neun, L. Tan-Sien-Hee, K. Ulman, Silicones as Excipients for Topical Pharmaceutical Applications – The Silky Touch Product Family from Dow Corning, Dow Corning Corp, (2002).
[4] FAO/WHO. Evaluation of certain food additives. Twenty-third report of the joint FAO/WHO Expert Committee on Food Additives. World Health Organ Tech Rep Ser 2014; No. 70.
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