Registration Dossier

Physical & Chemical properties

Endpoint summary

Administrative data

Description of key information

Additional information

Dodecamethylcyclohexasiloxane (D6) is a liquid at standard temperature and pressure, with a melting point of -3°C, and a boiling point of 245°C. It has a density slightly less than that of water (0.98 g/cm3at 20°C) and a kinematic viscosity value of 5.6 mm2/s at 20°C. It has a predicted vapour pressure of 4.7 Pa at 25°C.

The substance is not classified for flammability on the basis of a measured flash point 91°C and boiling point of 245°C in accordance with Regulation (EC) No. 1272/2008. D6 has a measured autoignition temperature of 368-371°C and it is not explosive and not oxidising on the basis of structural examination.

In contact with water, D6 will hydrolyse very slowly with a hydrolysis half-life of 42 h at pH 4, approximately 9600 h (401 days) at pH 7 and 125 h at pH 9 and 25°C. The product of hydrolysis is dimethylsilanediol.

[-Si(CH3)2O-]5+ 5H2O → 6(CH3)2Si(OH)2

D6 has low water solubility (ca. 5 µg/l at 23°C) and high log Kow (8.87). Based on an examination of the chemical structure, the substance is expected not to have an acid/base dissociation in water. Further testing for water-based physicochemical properties is waived due to the low solubility.