Registration Dossier

Physical & Chemical properties

Endpoint summary

Administrative data

Description of key information

Additional information

Hexamethyldisiloxane is a liquid at standard temperature and pressure, with a measured melting point of -68.2°C, and a measured boiling point of 100.5°C. It has a measured density of 0.76 g/cm3 at 20°C and moderate kinematic viscosity of 0.65 mm2/s at 25°C. It is highly volatile with a measured vapour pressure of 5500 Pa at 25°C.

The substance is classified as highly flammable on the basis of a measured flash point of -6°C and boiling point of 100.5°C. It has an auto-ignition temperature of 340°C, is not explosive and is not oxidising on the basis of structural examination.

In contact with water, hexamethyldisiloxane reacts slowly, half-life of 116 h (5 days) at pH 7 and 24.8°C according to the following equation:

(CH3)3SiOSi(CH3)3+ H2O → 2(CH3)3SiOH 

Hexamethyldisiloxane is slightly soluble in water (water solubility of 0.93 mg/l at 23°C) and has a measured log Kow of 5.06 at 20°C. It does not dissociate in solution nor show significant surface activity.