Phenyl and fluoro substituted silicones investigated

Evaluating technologies from other industries and applying them to personal care ingredients can provide a unique competitive edge. High refractive index silicones are used across many industries, from engineering applications in fibre optics and electronics to medical device applications in vision care. Light emitting diodes (LEDs) are made brighter and more efficient by coupling the high refractive index (RI) silicone to the light generating die, increasing light output. High RI silicones can increase the ability to manipulate and focus light for applications such as small but powerful intraocular lenses (IOLs), implantable lenses in the human eye to restore clear vision. These same properties are used to achieve benefits found in electronics, vision care, and cosmetic and custom formulations.

Silicone chemistry

Silicone polymers are an essential component of a silicone formulation. Figure 1 displays the typical structure of a silicone polymer consisting of regular repeating units of silicon and oxygen that create a polysiloxane backbone. This structure allows polysiloxanes to be used in a wide array of applications because various substituent groups (R) can be incorporated onto the polymer. Methyl is the most common substituent group found in cosmetic formulations and biomedical applications. It is most known for its water resistance and desirable surface properties. Other common organic groups that can be attached to the silicon atom include trifluoropropyl (-CH2CH2CF3) and phenyl groups (-C6H6). By substituting the methyl groups with phenyl or trifluoropropyl organic groups, certain properties of the silicone can be enhanced. For example, silicones possess high thermal stability and radiation resistance that increases with the replacement of methyl with phenyl. These attributes aid hair styling systems in resisting damage from intense styling, increase moisture via its lubricious nature, and protect against every day environmental conditions. Silicones are widely used in skin care formulations for basic moisturising properties. In an arid environment, heavier formulations are not desired, but phenyl can aid in providing a stronger occlusive barrier. It is the nature of the bulky carbon group (phenyl and fluoro) that aids in reducing moisture loss over the thin silicone deposition. Silicone polymers are oleophobic, a physical property that can be significantly increased by substitution of the methyl groups with increasing amounts of trifluoropropyl groups. Because fluorosilicones exhibit greater resistance to hydrocarbons9 such as solvents and oils, they make ideal coatings, seals, and gaskets when a standard dimethicone would swell and deteriorate. Crossover or transfer technology allows the formulator to take what is known about an existing ingredient, and broaden the abilities of that ingredient. By evaluating some of the benefits of silicones used in other industries, correlations can be attributed back to the personal care industry.