Industry expert Tony O'Lenick asks: What's the difference between dimethicone and alkyl dimethicone? Rick Vrckovnik of Siltech LLC reponds.
Dimethicones, otherwise known as silicone fluid or polydimethylsiloxane fluid, are silicone homo-polymers. They are non-reactive and available with varying molecular weights. The products generally are sold by viscosity, which is determined by molecular weight. The structure is shown below.
Dimethicone polymers are liquids and are not soluble in water or oil. In pure compounds, the viscosity of the dimethicone varies directly with the value of “x.” Dimethicone exhibits good thermal stability and low surface tension.
In the personal care industry, dimethicones are widely used as conditioners in shampoos. Dimethicone provides skin protection and when used in this application are considered drugs.
Alkyl dimethicones, in contrast, are silicone hetero-polymers that have a long chain alkyl group grafted onto the silicone backbone. The structure is shown below.
Alkyl dimethicones are made by the hydrosilation reaction of a silicone hydride fluid with an olefin containing terminal double bond. They are not water-soluble, but can be either silicone- or oil-soluble, depending on the ratio of x, y and z. The higher the value of x and the lower the value of z, the more silicone soluble it will be; and the higher value of y and z, the more oil soluble it will be.
As well, by varying the ratio of x, y and z, one can make an alkyl dimethicone that is liquid, a soft paste or a hard wax. Generally, if one uses an olefin with 22 or higher alkyl groups, the product will be a paste or hard wax, depending on the ratio of x to y. The higher the value of x, the lower the melt point of the product.
When one uses an olefin with 18 carbon groups, the alkyl dimethicone can be a liquid to hard wax, depending on the ratio of x to y. Alkyl groups with 16 carbon groups or lower are normally liquids to soft pastes. Alkyl dimethicone provides cosmetic elegance to formulations containing them. They also improve SPF values when added to sunscreens.
The alkyl dimethicones are used when silicone feel and conditioning is desired from an oil or ester based product for which the dimethicones are not soluble. They can also be used in silicone based systems to provide the feel of esters and oils.
Alkyl Dimethicone structure: