Dimethicone (Polydimethylsiloxane)

Dimethicone – Versatile Silicone Conditioner and Protectant for Cosmetics and Pharmaceuticals

Basic Information

• CAS Number: 9006-65-9

• Chemical Name: Polydimethylsiloxane

• Molecular Formula: [–Si(CH₃)₂–O–]ₙ

• Appearance: Clear, colorless, viscous liquid (viscosity varies by grade)

• Odor: Practically odorless

• Solubility: Insoluble in water; miscible with oils and organic solvents

• Specific Gravity: 0.95–0.98 g/cm³ (depending on viscosity)

• Flash Point: >100°C (depending on viscosity)

• Storage: Store in tightly sealed containers in a cool, dry place, protected from light and moisture

Overview
Dimethicone (polydimethylsiloxane) is a linear silicone polymer widely used in cosmetic, personal care, and pharmaceutical formulations. Its inert, non-reactive nature, combined with excellent spreading, lubricating, and film-forming properties, makes it a versatile ingredient for skin and hair care products. It provides a smooth, silky, non-greasy feel, protects the skin from moisture loss, and improves the performance and sensory qualities of formulations.

Synthesis
Dimethicone is synthesized by hydrolysis and polycondensation of dimethyldichlorosilane ((CH₃)₂SiCl₂), followed by polymerization to achieve the desired molecular weight and viscosity. The degree of polymerization can be controlled to produce a wide range of viscosities, from low-viscosity fluids to high-viscosity gums.

Physicochemical Properties

• Inert and stable: Does not react with most cosmetic ingredients; resistant to oxidation and degradation.

• Film-forming: Creates a breathable, water-resistant barrier on skin and hair.

• Lubricating: Provides excellent slip and spreadability, improving product application.

• Non-greasy: Leaves a smooth, silky feel without oiliness or tackiness.

• Water-repellent: Reduces moisture loss and protects against environmental factors.

• Hypoallergenic: Well-tolerated by sensitive skin; non-comedogenic.

• Compatibility: Miscible with most oils, esters, and other silicones.

Applications

• Skin care: Moisturizers, serums, sunscreens, and anti-aging creams – provides smoothness, hydration, and a protective barrier.

• Hair care: Shampoos, conditioners, serums, and styling products – adds shine, reduces frizz, improves manageability, and protects against heat damage.

• Color cosmetics: Foundations, primers, lipsticks, and mascaras – improves pigment dispersion, application, and long-wear properties.

• Baby care: Diaper creams, lotions, and ointments – soothes and protects delicate skin.

• Pharmaceuticals: Used as an excipient in topical ointments, creams, and protective barrier formulations.

• Antifoaming agents: Used in industrial and food applications to reduce foam formation.

Key Benefits

• Provides excellent conditioning and smoothing properties for skin and hair.

• Forms a protective, breathable film that retains moisture.

• Improves spreadability, slip, and sensory feel of formulations.

• Non-irritating, hypoallergenic, and safe for sensitive skin.

• Compatible with a wide range of cosmetic and pharmaceutical ingredients.

• Available in various viscosities for tailored performance.

• Stable and resistant to oxidation and degradation.

• Enhances product texture, application, and wear.

Recommended Use
Typical usage levels vary widely depending on the application and desired viscosity:

• Skin care: 1–10% of the formulation.

• Hair care: 1–5% for conditioners and serums.

• Color cosmetics: 1–15% for improved texture and wear.

• For optimal performance, incorporate into the oil phase at room temperature or with gentle heating. Can be combined with other silicones, oils, and emulsifiers for tailored formulations.

Safety and Handling

• Generally recognized as safe for use in cosmetics and pharmaceuticals at recommended concentrations.

• Low irritation potential; well-tolerated by skin and eyes.

• Avoid contact with strong oxidizers.

• Store in a cool, dry place, away from direct sunlight and heat sources.

• Use appropriate personal protective equipment (gloves, safety goggles) when handling.

• Shelf life: typically 24–36 months under recommended storage conditions.

Quality Assurance
Each batch is tested for viscosity, purity, and volatile content to ensure consistent quality and compliance with cosmetic and pharmaceutical standards.