Hexamethyldisiloxane

Hexamethyldisiloxane is a chemical compound with the formula O[Si(CH3)3]2. This volatile liquid is used as a solvent and as a reagent. The species arises by the hydrolysis of trimethylsilyl chloride. The molecule is the protypical silyl ether and can be considered a subunit of polydimethylsiloxane.

Uses
It is primarily used as source of the trimethylsilyl functional group (-Si(CH3)3) in organic synthesis. For example, in the presence of acid catalyst, it converts alcohols and carboxylic acids into the silyl ethers and silyl esters, respectively.

Miscellaneous uses
HMDS is used as an internal standard for calibrating chemical shift in 1H NMR spectroscopy. It is more easily handled since it is less volatile than the usual standard tetramethylsilane but still displays only a singlet near 0 ppm.

HMDS has even poorer solvating power than alkanes. It is therefore sometimes employed to crystallize highly lipophilic compounds.

it is also used in liquid bandages (spray on plasters) like in cavilon spray used on the body to protect damaged skin from irritation from other bodily fluids

Safety
Like most siloxanes, hexamethyldisiloxane is fairly innocuous.