Ingredient Profile—Dimethicone

Apr 1, 2012 | Contact Author | By: Michael J. Fevola, PhD, Johnson & Johnson Consumer and Personal Products Worldwide
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Title: Ingredient Profile—Dimethicone
siliconex dimethiconex sensoryx hairx skinx
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Keywords: silicone | dimethicone | sensory | hair | skin

Abstract: Polydimethylsiloxane (PDMS), more commonly known as dimethicone, is the most widely utilized silicone material in cosmetics and personal care. It is found in a wide variety of rinse-off and leave-on products such as shampoos, hair conditioners, skin moisturizers and color cosmetics.

Market Data

  • Sales for hair care climbed 6% in 2012.
  • Shampoo, conditioners and colorants were all winners, although relaxants and hair loss treatments were a bit of a disappointment.
  • Emerging market continue to be the growth driver, fueling 92% of growth in absolute terms in 2012.
  • The BRICs—particularly China, India and Brazil—continue to be top drivers.
  • Second-tier markets, such as Turkey, are also beginning to attract more attention.
  • Hair care brands have an opportunity to develop products that attract second-tier markets and pick up some of the dollars that are no longer being spent in salons.
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Polydimethylsiloxane (PDMS), more commonly known as dimethicone, is the most widely utilized silicone material in cosmetics and personal care.1, 2 It is found in a wide variety of rinse-off and leave-on products such as shampoos, hair conditioners, skin moisturizers and color cosmetics.3, 4 Despite its relatively simple chemical structure, dimethicone exhibits unique physical properties that render it effective for conditioning and protecting the hair and skin, and improving the sensorial attributes of formulations. Dimethicone is also a key component of hundreds of modified silicones, which represent some of the most sophisticated and high performance ingredients available today.

Chemistry

Dimethicone is a hybrid inorganic-organic homopolymer comprised of dimethylsiloxane repeat units, i.e., the polymer consists of an inorganic siloxane backbone (–Si–O–) that bears two methyl (–CH3) groups on each silicon (Si) atom. According to the International Cosmetic Ingredient Dictionary & Handbook, the name dimethicone refers specifically to fully methylated PDMS homopolymers that are end-capped with trimethylsiloxy (TMS) groups.3 Other International Nomenclature of Cosmetic Ingredients (INCI) names are used to refer to PDMS homopolymers with different end-groups. For example, hydroxyl (–OH) end-capped PDMS is called dimethiconol, and hydrogen end-capped PDMS is called bis-hydrogen dimethicone.

The degree of polymerization (DP) can span several orders of magnitude for dimethicone. Thus, n can be as low as 0–3 for the volatile silicones, to as high as several thousand for high viscosity silicone gums.1 Note that when n = 0 and n = 1, the INCI names for the compounds are disiloxane and trisiloxane, respectively.

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This content is adapted from an article in GCI Magazine. The original version can be found here.

 

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Figure 4. Acid-catalyzed equilibrium polymerization of D4 to produce dimethicone

Figure 4. Acid-catalyzed equilibrium polymerization of D4 to produce dimethicone

Figure 5. Condensation polymerization of low MW silanol-terminated linear PDMS oligomers

Figure 5. Condensation polymerization of low MW silanol-terminated linear PDMS oligomers followed by end-capping to produce dimethicone

Figure 1. Chemical structure of dimethicone

Figure 1. Chemical structure of dimethicone

Figure 2. a) Carbothermic reduction of SiO2 to Si metal and b) direct process for synthesis of methylchlorosilanes

Figure 2. a) Carbothermic reduction of SiO2 to Si metal and b) direct process for synthesis of methylchlorosilanes

Figure 3. Hydrolysis of dimethyldichlorosilane

Figure 3. Hydrolysis of dimethyldichlorosilane (DCDMS) to produce cyclic and linear silanol-terminated PDMS oligomers

Centipoise (cP) vs. Centistokes (cSt)

Formulators typically report viscosity values in units of centipoise (cP), which is a unit of dynamic viscosity (η) in the centimeter gram second (cgs) system of units; one cP = 0.01 g·cm-1·s-1. However, the viscosities of dimethicone fluids are reported in units of centistokes (cSt), which are units of kinematic viscosity (μ); one cSt = 0.01 cm2·s-1. A fluid’s dynamic viscosity at a given temperature is simply its kinematic viscosity multiplied by its density (ρ) at that temperature:

η = μ · ρ

For example, a dimethicone fluid with a kinematic viscosity of 100 cSt and a density of 0.964 g·cm-3 at 25°C would have a dynamic viscosity of 96.4 cP. Kinematic viscosity is commonly measured by using a calibrated glass capillary viscometer, whereas measurements of dynamic viscosities require more sophisticated instruments such as rheometers or rotational viscometers, e.g., a Brookfield viscometer.

Biography: Michael J. Fevola, PhD, Johnson & Johnson

Michael J. Fevola, PhD, is a manager in the New Technologies group at Johnson & Johnson Consumer and Personal Products Worldwide in Skillman, NJ, where he leads R&D in polymer and surface chemistry. Fevola has authored 12 peer-reviewed articles and book chapters, is an inventor on six US patents, and is a member of the Personal Care Product Council’s International Nomenclature Committee and the Society of Cosmetic Chemists.

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