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April 27, 2011

Amodimethicone and other Amine Silicones


Tonya McKay of NaturallyCurly writes;

For people with curly hair, silicones elicit many emotions. For some, they are a holy grail ingredient, while others shy away from them for fear they will dry out their hair.

It is evident that there exists a considerable amount of confusion in the curly community in regard to whether silicones are good for curly hair and compatible with shampoo free hair care routines.

In this column, we’ll take a look at amodimethicone and other similar molecules, such as bis-aminopropyl dimethicone and trimethyl silylamodimethicone. And we’ll talk about the pros and cons of using them, especially if you shy away from sulfates.

These are being used more often by chemists as conditioning agents in hair product formulations. They are popular because of their ease of use in processing and manufacturing products as well as for their many benefits to the hair.

Amodimethicone is an abbreviation of “amine-functionalized silicone,” which is a family of silicones modified to have specific properties. The simplest, and perhaps most well-known silicone, polydimethylsiloxane (dimethicone, by INCI naming standards), consists of methyl groups (-CH3) as the pendant group along the backbone of the polymer chain (Figure 1). Amine-functionalized silicones have been chemically modified so that some of the pendant groups along the backbone have been replaced with various alkylamine groups (-R-NH2). These amine groups become positively charged in aqueous solutions because of their electron-donating (basic) tendencies, yielding an inorganic, cationic polymer.

These inorganic cationic polymers deposit onto the hair because of the electrostatic attraction between the polymer and the negatively-charged protein surface of the cuticle. In this manner, they behave much like polyquaternium materials (organic cationic polymers), which are excellent conditioning agents as well. The charge density of the polymer can be varied by changing the placement and quantity of the amine groups. A polymer with greater charge density will be more substantive to the hair than one with lesser charge density.

One interesting property of these polymers is that they provide selective conditioning to the areas most in need of it. The mechanism by which they accomplish this is, again, electrostatic attraction. Highly damaged areas of the hair cuticle possess higher negative charge density, which enhances the affinity of the cationic polymer to that specific area. These polymers can provide a targeted beneficial effect.

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