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Dow Corning® Silicone Elastomer Blends made with Non-Silicone Solvents and Their Applications in Formulations

IP.com Disclosure Number: IPCOM000126769D
Publication Date: 2005-Jul-30
Document File: 9 page(s) / 178K

Publishing Venue

The IP.com Prior Art Database

Abstract

The use of silicone elastomer blends in personal care formulations has increased steadily since these blends were first introduced in the 1990's. A silicone elastomer blend consists of a crosslinked silicone polymer (elastomer) that is blended with a solvent that is sufficiently compatible with the silicone elastomer that the solvent swells the silicone elastomer. Such an elastomer/solvent blend has the form of swollen elastomer particles where the solvent is entrapped within the elastomer matrix. These swollen gel particles have a very desirable skin feel as well as other benefits on the formulation such as rheology modification (thickening). We have found that when silicone elastomer blends are made with non-silicone solvents, these blends have better performance and esthetics when these elastomer blends are used in formulations with oil-soluble active ingredients such as sunscreen oils, natural lipids, and oil-soluble vitamins and vitamin derivatives.

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Silicone Elastomer Blends made with Non-Silicone Solvents and Their Applications in Formulations

The use of silicone elastomer blends in personal care formulations has increased steadily since these blends were first introduced in the 1990’s.  A silicone elastomer blend consists of a crosslinked silicone polymer (elastomer) that is blended with a solvent that is sufficiently compatible with the silicone elastomer that the solvent swells the silicone elastomer.  Such an elastomer/solvent blend has the form of swollen elastomer particles where the solvent is entrapped within the elastomer matrix.  These swollen gel particles have a very desirable skin feel as well as other benefits on the formulation such as rheology modification (thickening).

Note that for consistency and clarity, materials in this disclosure are referred to by their International Cosmetic Ingredient (INCI) name.  INCI names are assigned by the Cosmetic Toiletry, and Fragrance Association for materials that are used in cosmetic applications.  INCI names are recognized in most major markets around the world.

Most commercial silicone elastomer blends utilize silicone solvents such as cyclopentasiloxane, cyclotetrasiloxane, or dimethicone.  However in certain kinds of personal care formulations such as those that include sunscreen oils, silicone elastomer blends that contain silicone solvents do not provide the expected benefits.  The problem seems to be incompatibility between the sunscreen oils, the silicone solvent, and the silicone elastomer.  If sunscreen oils such as ethylhexyl methoxycinnamate (octinoxate) are mixed with silicone elastomer blends that contain cyclopentasiloxane, the incompatibility is indicated by a change in clarity and a loss in viscosity, which is presumably caused by de-swelling of the elastomer gel particles.  In order to avoid this problem, the possibility of producing silicone elastomer blends with non-silicone solvents was tested.

A series of silicone elastomer blends were made by reacting an SiH functional polysiloxane with an alpha,omega-diene.  The procedure for making these blends is described in U.S. Patent 5,654,362 (Schulz and Zhang).  The silicone elastomer made using this reaction is known as dimethicone crosspolymer.  The reaction was conducted in a solvent or blend of solvents in the presence of a platinum catalyst.  The gel was cured at an elevated temperature and then sheared to produce gel particles.  Additional solvent and an excess of a vinyl terminated siloxane (to consume residual Si-H) were added to the gel and the mixture was sheared to form a paste.  The active, ethylhexyl methoxycinnamate , was added to the paste with additional solvent to reach the desired proportions of active, elastomer, and solvent.  All samples were prepared following the procedures described in examples 1 and 2.

Solvents tested included isododecane, isodecyl neopentanoate, and  cyclopentasiloxane.  Samples were compared for clarity by...