S

Figure 17 Results of hair swatch test for thick hair.

This created additional demand for silicone derivatives that are multifunctional. The basic backbone remains the same (Si—O—Si); however, the options for derivatization range from simple pendent alkyl chains to complex a, ra-poly-alkoxylated structures with additional functionality such as quaternized nitrogen or amines. Modified silicones provide increased performance through enhanced sub-stantivity, increased emulsion stability, better shine, increased wetting time, and improved rheological control and film-forming deposition properties on hair. These properties are directly related to the type of functional group substituted and the mole percent of this substitution on the backbone. The main silicone derivatives to be discussed are the alkyl siloxanes, dimethicone copolyols and quaternary silicones.

3.1 Alkyl-Modified Silicones

Modified silicones are easier to handle and offer greater functionality and versatility. The particular class of alkyl-modified silicones (cetyl dimethicone) offer improved formulation stability in addition to film-forming properties and increased spreading rates. As is often the case, alkyl-modified siloxanes were not developed for the cosmetic industry, but borrowed from an industrial application [23]. Like many raw materials, they were adapted to suit the cosmetic industry. They are prepared by substitution of an alkyl group on the linear polydimethyl-siloxane (PDMS) backbone. The physical form of this class of raw materials ranges from oils low in viscosity to high melting solids. Naturally, this is dependent upon the alkyl chain length, its distribution, branching, and degree of substitution, in addition to the properties of the polymer backbone. These materials do not give the typical greasy properties of organic waxes. They impart thickening for most emulsion types and give body and cushion to the end formulation. The polymeric backbone is responsible for the loss of greasy tact and substitutes the typical "silicone" feel [24]. The alkyl moeity is responsible for formulation stability, flexibility, and compatibility with organic additives.

The synthesis of organosilicone water-in-oil emulsifiers is based upon the linkage of polymethylsiloxane chains with alkyl side chains and polyglycol groups. The polymethylsiloxane chain possess both hydrophilic and lipophilic characteristics. The polyglycol groups provide the necessary hydrophilic characteristics, and the side chains provide lipophilicity. The performance properties may be easily adjusted by varying the side chain, the siloxane backbone, and the ethylene oxide/propylene oxide content. The high functionality of these materials |

is likely due to the strong absorption at the phase boundaries. The requirements of multifunctional hydrophobic emulsifiers are best provided by polymeric materials. These requirements are easily met by the polyalkyl polyether polysiloxane copolymers. They are active at a level of 1-3% and form very thin interfacial films. |

They are highly flexible toward interfacial stress.

One class of lipophilic emollients of particular interest is the polyalkyl poly-siloxane copolymers. It is known that polyalkyl-modified polysiloxanes are compatible with emollients, waxes, and other silicone polymers. They are excellent additives for improving the slip properties of emulsions. Simple combination of a variety of examples from this class with typical emollients such as isopropyl myristate, octyl stearate, and caprylic/capric triglycerides were compared for their spreading. The addition of 0.1% w/w of cetyl dimethicone (as ABIL Wax 9840) reduced the surface tensions of simple emollient esters by 20%, for instance. Furthermore, the uniform deposition of traditional actives and quaternaries onto hair is improved by these alkyl-modified siloxanes [24].

3.2 Cationic Polydimethyl Siloxane

Incorporation of cationic or amphoteric groups into the copolyol leads to increased substantivity toward polar substrates. This provides the deposition of a durable film onto the surface of the hair shaft. Polydimethylsiloxanes modified with cationic groups combine a high gliding ability with marked antistatic properties. Polyether side chains may also be included in addition to the ionic groups to improve the solubility and compatibility in formulation.

Silicone quaternary compounds provide excellent conditioning with the added benefit of mildness. This is a feature not generally shared with their traditional counterparts (quaternary ammonium compounds). Since the silicone quaternaries are relatively expensive, they are not used widely as replacements, but rather as additives (0.2-0.4%), to improve the tactile properties.

Quaternium-80 is a diamidoquaternary polydimethyl siloxane somewhat intermediate between traditional quaternary ammonium compounds such as palmitamidopropyltrimonium chloride and silicones (Fig. 18). This molecule combines the best of both worlds. The excellent static control property of amido quaternaries is retained, as well as the film-forming properties of silicones. In addition, quaternium-80G is compatible with anionic surfactants, making it highly suitable for two-in-one shampoos. The charge density of quaternium-80 is much lower than that of traditional cationics, however. This can be easily overcome through combination. Several similar hair rinse formulations were prepared and

Figure 18 Quaternium-80.

Figure 18 Quaternium-80.

assayed for the performance properties. These included sensory evaluations, half-head tests, wet and dry combing force measurements, volume force measurements, and gloss determination. The active components of conditioning agents were kept at 2.0%.

First, a hair swatch test was used to compare sensory conditioning properties such as wet comb, dry comb, dry feel, and flyaway behavior using the test formulations of Table 8. Both, virgin Caucasian (European) bundled hair (2 g weight, 18 cm length) and virgin Asian (Chinese) bundled hair (3 g weight, 18 cm length) were purchased (Kerling, Germany). The hair tresses were subjected to predam-age by means of permanents and bleaches using trade standard products (Wella). Tap water (37°C, 8°dH = 80 mg CaO/L H2O) was used to wet the hair. One gram of test formulation was then applied to each hair tress, and carefully worked into the tress. Following an action period of 1 minute, the hair was rinsed with tap water (37°C, 8°dH) for 1 minute After the excess water had been pressed out with a towel, the wet hair was assessed directly by means of a precisely defined system of criteria. This system of assessment criteria gives assessment marks for each characteristic property. Here, "5" designates an excellent assessment, "1" means that there is deficiency. Following an assessment of wet comb, the hair tresses were dried overnight at 25°C and 50% relative humidity in a hanging position. The same system of assessment criteria was again used to assess the dry comb and dry feel. The results of the test with Caucasian hair showed that cetrimonium chloride, stearamidopropyl dimethylamine, and the combination of stearyldimethylamine and quaternium-80 gave comparable conditioning results [25]. Independently, the formulation with quaternium-80 alone does not appear to perform as well as the cationics for the property of dry comb [25]. On Asian hair, the test formulas performed similarly except that a small advantage was noted for the combination of stearamidopropyl dimethylamine and quaternium-80 [25].

In addition to the sensory test performed on hair tresses, the shadow contour method was used to indirectly measure the static charge on the hair tresses [25]. This test was performed at constant temperature and humidity. Each hair tress was hung in front of a concentric measuring scale. A single point light, at a defined distance, was used to project the shadow of the hair tress. The hair was charged by defined combing and the shadow contour measured for each hair tress. The results for both Caucasian and Asian hair are given in Fig. 19.

All test formulations gave similar responses with the exception of quater-nium-80 on Asian hair. This may be explained by the difference in charge density of the silicone derivative in comparison to the traditional molecules. The performance of quaternium-80 on Caucasian hair may be explained by a film-forming lubrication effect rather than by antistatic behavior due to charge [25]. Because Asian hair is more structured and thick, the effect of the silicone is not as dramatic.

Furthermore a half-head test with a trained hairdresser was carried out on the foregoing formulations. For that cetrimonium chloride (CTAC) was compared

Figure 19 Flyaway by shadow contour method.

with stearamidopropyl dimethylamine (SDMA) quaternium-80, and the combination according the properties shown in Fig. 19. Between CTAC and SDMA no statistical difference for all tested parameters was found. Quaternium-80 gave a significantly better wet combability and an arguably better gloss. The results of the combination compared to CTAC are given in a radial graph (Fig. 20). Specifically, the wet comb property was enhanced for the combination (quaternium-80 and stearamidopropyl dimethylamine), rather than for the single ingredients [25].

The body/volume force of quaternium-80 toward hair was assayed in accordance with a standard method [26]. All formulations in Table 7 were tested with this method. The results indicated that quaternium-80 was equivalent to a standard cationic for reduction of body (Fig. 21). Quaternium-80 and CTAC reduced the body force measurements the most significantly. This is further evidence for the deposition properties of quaternium-80.

3.3 Polyether Polysiloxanes

Typically, polyether polysiloxane copolymers have pendent structures (Fig. 22). In these copolymers, the performance that is expected from the silicone moiety is often masked. The silicone backbone is free to rotate, while at the same time the repeating polyether is free to wrap around the silicone backbone. This may explain the lack in performance of these materials in comparison to the a,ra-derived |

copolymers (Fig. 17). A new dimethicone copolyol was prepared by using the sil- :§

icone backbone of quaternium-80 and derivatizing a and ra with a 40:60 ratio of ^

ethylene oxide to propylene oxide (Fig. 23) [27]. This structure was selected based |

upon the surface tension measurement of several analogues in aqueous sodium t

Figure 20 Comparative results from salon test.

dry feci

(5 = excellent; 1 = very deficient) CTAC

Figure 20 Comparative results from salon test.

Table 7 Active Ingredients in Test Formulations3

Ceteareth-25 Cetyl alcohol CTAC SDMA Quaternium-80 Water

Active ingredients (%)

Quaternium-CTACl SDMA 80

SDMA/ quaternium-

80 Placebo

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