The Use of Cationizing Reagents in the Preparation of Conditioning Polymers for Hair and Skin Care

Cationic compounds with quaternary ammonium functional groups are used extensively in personal care product applications. One important class of such quaternary ammonium compounds is cationically charge-modified polymers derived from various animal and plant sources, including guar gum, cellulose, proteins, polypeptides, chitosan, lanolin, starches and amino silicones. These polymers have a demonstrated utility as substantive conditioning agents in hair care formulations and have also found wide acceptance in skin care products. Cationic conditioners are known to revitalize the hair: protecting against environmental damage and offseting the physical stress created by daily styling procedures such as blowdrying, bleaching, coloring, combing and perming. These cationic derivatives act as conditioning and thickening agents in hair care applications and also exhibit skin protection properties, due to their functional surface properties and their emollient smooth feel. An overview of cationizing reagent chemistry and the various commercial methods for producing cationic conditioning polymers are described. The Conditioning Mechanism A product is considered to be a conditioner if it improves the quality of the surface to which it is applied, particularly if this improvement involves the correction or prevention of certain aspects associated with surface damage. Conditioning of the hair and skin must be a continuous process, as both substrates are in a constant cycle of shedding and renewal. The main difference between hair and skin is that skin is basically a living organ that replaces its outermost layer on a frequent basis. Hair, in contrast, is basically dead material derived from a few live cells deep within the skin surface. Thus, conditioning agents for skin can affect the homeostatic processes of growth and repair by supplementing the body’s renewal mechanisms. Conditioning agents for hair have no effect on growth and cannot affect cellular repair. Rather, they can only temporarily improve the cosmetic appearance of damaged hair and must be reapplied as removal occurs. For skin to appear and feel normal, the moisture content of the upper layer must be above 10%. Moisture is lost through evaporation under low humidity conditions and must be replenished with water from the lower epidermal and dermal layers. Once skin damage has occurred and the barrier has been damaged, reconditioning can occur only if the loss of moisture is retarded. This is the goal of moisturizers, which function temporarily until skin integrity can be re-established. Page 1 of 10 Hair damage results from both mechanical and chemical treatments that alter any of the physical structures of the hair. Conditioning agents cannot enhance repair, but can temporarily increase the cosmetic value and function of the hair shaft until removal of the conditioner occurs with cleansing. Most hair damage occurs as a result of grooming habits and exposure to chemicals used for esthetic purposes, such as shampooing, drying, combing, brushing, styling, dyeing, permanent waving, and to environmental factors, such as sunlight, air pollution, wind, seawater, and chlorinated swimming pool water. There are several mechanisms by which conditioners can improve the cosmetic value of the weathered hair shaft by increasing shine, decreasing static electricity, improving hair strength and protecting against ultraviolet radiation. Conditioning the hair can mitigate this hair damage by improving sheen, decreasing brittleness, decreasing porosity, and increasing strength. Polymeric conditioners help hair and skin look and feel better by improving the physical condition of these surfaces. Hair conditioners are intended primarily to make wet hair easier to detangle and comb and to make dry hair smoother, shinier, and more manageable. Skin conditioners primarily moisturize, while providing protection from the drying effects of the sun, wind, and contact with harsh detergents. Cationic polymers are very efficacious conditioning agents because of their substantivity to the respective substrate, which is directly attributable to electrostatic interactions between oppositely charged sites on the hair shaft or skin surface and on the polymer backbone. Conditioners typically remain on the fiber surface, reducing combing forces and flyaway, and in some systems, providing enhancement of volume, curl retention, body and manageability. Modern conditioners are designed to provide one or more of the following functions: • provide ease of wet and dry combing • smooth, seal and realign damaged areas of the hair shaft • minimize porosity • impart sheen and a silken feel to the hair • provide some protection against thermal and mechanical damage • moisturize • add volume and body • eliminate static electricity Production of Conditioning Polymers Using Cationic Reagents The oligomers or polymers used as the chemical precursors for cationic conditioning agents contain either hydroxyl, amino or mercapto functional groups as part of their monomer structure. These reactive groups are available for a wide range of chemical reactions, such as etherification or esterification. In the case of the cationic moieties, quaternary ammonium groups are grafted onto the polymer backbone and become covalently bound. These cationic groups enhance the polymer’s substantivity to anionic substrates, such as hair and skin. The introduction of longer chain alkylquat groups onto the polymer substrate produces a family of products having distinct physical and conditioning properties. Here, the effect of a cationic substrate is combined with functional properties normally associated with fatty acid quats like manageability, lubricity, anti-static properties, surface activity and biocidal activity. The reagent products that are used for the cationic modification of polymeric substrates are quaternary ammonium salts with a reactive chemical end-group. They are commercially available in the stable chlorohydrin form or, in the case of the trimethylammonium reagent, also in the reactive epoxide form. The range of commercially available cationizing reagent products is shown below in Table 1.