What Is Hexamethyldisiloxane (HMDSO)?

2026-08-21

Hexamethyldisiloxane, commonly abbreviated as HMDSO (CAS 107-46-0), is a colourless, transparent liquid with a density of approximately 0.8 g/cm³, a boiling point of approximately 100°C, a melting point of -59°C, and a flash point of approximately -2°C. It is insoluble in water but soluble in most organic solvents. Industrially, it is used as a capping agent, cleaning agent, and release agent; it is employed in the manufacture of silicone oil, silicone rubber, and other silicone products; it also serves as a water-repellent agent for fabric surface treatment and moisture protection of components; and it can function as a stationary phase in gas chromatography. In the field of scientific research, HMDSO can serve as a precursor for depositing silicon oxide (SiOx) coatings on substrate surfaces using technologies such as plasma chemical vapour deposition. It is classified as a flammable liquid (Hazard Class 3) and must be stored in a cool, dry, and well-ventilated environment, away from sources of ignition and heat, and separated from oxidizing agents.

How to Make Hexamethyldisiloxane?

The laboratory preparation method involves adding 62.49 g (0.575 mol) of trimethylchlorosilane dropwise to a solution consisting of 72.7 g (0.06 mol) of N, N-dimethylaniline and 7 g of water. The mixture is heated and refluxed for 1 hour, then distilled under atmospheric pressure. The fraction collected at 98–101°C is dried to yield hexamethyldisiloxane, with a yield of 43–44 g (92–94%). In industrial production, trimethylchlorosilane is hydrolysed at 30–40 °C.

What Are the Properties of Hexamethyldisiloxane?

Melting point	−59 °C (lit.)
Boiling point	101°C (lit.)
Density	0.764 g/mL at 20 °C (lit.)
vapor density	>1 (vs air)
vapor pressure	20 hPa (20 °C)
refractive index	in 1.377 (lit.)
Flash point	33 °F
storage temp.	Store below +30°C.
solubility	0.00037 g/l insoluble
Viscosity	0.65 cSt (25°C)
Water Solubility	insoluble

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Risk and Safety Statements

Symbol(GHS)	GHS02, GHS09
Signal word	Danger
Hazard statements	H410-H225
Precautionary statements	P501-P273-P240-P210-P233-P243-P241-P242-P280-P370+P378-P391-P303+P361+P353-P403+P235
PPE	Eyeshields, Faceshields, Gloves, type ABEK (EN14387) respirator filter
Hazard Codes	F, N, T
Risk Statements	11-50/53-65-51/53-48/23/24/25-36/38-46-45
Safety Statements	16-61-62-45-26-53
WGK Germany	3
Autoignition Temperature	340 °C
HazardClass	3
PackingGroup	II
Storage Class	3 - Flammable liquids

What Is Hexamethyldisiloxane Used For?

HMDSO is widely used in many traditional industrial sectors. In the silicone industry, it is primarily used as a chain-terminating agent and an important intermediate in the production of silicone products such as silicone oils, silicone rubbers, and silicone resins. In the field of surface treatment, it serves as a water-repellent agent for treating the surfaces of textile fibres and for providing insulation and moisture protection in radio components. In analytical chemistry, it is commonly used as a stationary phase in gas chromatography. In chemical manufacturing, it serves as a cleaning agent and demolding agent in organic and pharmaceutical chemical production. Additionally, it can be used as a circulating coolant for instruments and meters, as well as an analytical reagent, insulating material, and moisture-proofing agent.