Situ Polymerizations in Hair

Amino functional silicones, on the other hand, have been used in hair conditioners and shampoos for several years to improve hair conditioning. Because of the potential cationic charge on amino functional silicones, it is sometimes mistakenly accepted that all amino silicones are more substantive to hair than dimethicones. Several years ago we conducted a study among amodimethicones of varying molecular weight (about 1,000 to 

With the exception of oxidation hair dyes, in situ polymerizations in hair have been only laboratory and concept curiosities. However, remarkable changes to the chemical [79] and physical properties [80] of the fibers have already been achieved using this technology, and in the future, through the combination of science and imagination, some in situ polymerization hair treatment may end up in the marketplace. The remaining sections of this chapter describe oxidation dyes as in situ polymerization hair treatments and in situ vinyl polymerization reactions in human hair. 

Although not generally described as such, certain reactions of oxidation hair dyes are examples of in situ polymerizations in hair. These consist of the oxidation of electron-rich aromatic amine and phenol monomers that condense with each other and perhaps even attach to amino acid residues of hair. The net result, at least with products containing p-phenylenediamine (PPD) and resorcinol, is the formation of polyindophenol-type polymeric pigments [81-83] that render color to the hair. (See the discussion on oxidation hair dyes in Chapter 6 and its references for additional details.) 

Several techniques have been employed for the polymerization of vinyl monomers on and in wool fiber. 

Reduction of the fibers, followed by reaction with vinyl monomer and oxidizing agent in an inert atmosphere [84,85] 

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Other Chemical Modifications to Hair. Modification to the number of acidic and basic groups have been made by Laden and Rnkelstein [114], who added Bunte acid groups to hair, and by Robbins and Anzuino [115], who added polydimethylaminoethyl methacrylate groups to hair by in situ polymerization. 

The binding interactions of polymers to hair The chemical nature of polymers used in hair products In situ polymerization reaction mechanisms Rheological or flow properties of polymer solutions Film formation and adhesional properties of polymers... 

The major emphasis in this chapter is on the first three items—the chemical and/or binding interactions of polymers to hair the chemical nature of hairsprays, setting products, and mousses and the in situ polymerization reactions in hair. Although the rheological properties of polymer solutions are especially important to formula viscosity and to the sensory perceptions of cosmetics, they will not be emphasized here. It suffices to say that cellu-losic ethers [8, 9] are probably the most important thickening agents in hair products, and ethoxylated esters and carboxy vinyl polymers are also important. 

Primary valence bonds include ionic and covalent bonds and are the strongest binding forces. They generally have bond energies of approximately 50 to 200kcal/mole [17]. Ionic bonds are extremely important to the interactions of polymeric cationic ingredients and hair, whereas covalent bonds are probably involved between polymer and hair in certain in situ polymerization reactions or in the reaction of oxidation dyes with hair. 

Obviously, multiple sites for attachment of even stronger bonds (i.e., polar and especially primary valence bonds) are even more important to substan-tivity [22], Multiple covalent attachment sites could conceivably occur via in situ polymerization reactions and with bifunctional cross-linking agents. However, for pragmatic reasons, this is not nearly as important as multiple ionic attachments to hair (e.g., with cationic polymers). 

While not strictly considered emulsions, two other systems may be classified in this category, both of which comprise very small particles of silicone fluids in aqueous dispersions. The first method of preparing these microdroplets involves in situ polymerization of a water-soluble vinyl monomer or mixtures of said monomer and acryl comonomers. The silicone fluids are first dispersed into microdroplets in the water phase by means of high-speed agitation and then the vinyl monomers or cationic polymers are added at elevated temperatures in the presence of free-radical catalysts. The resulting aqueous polymer matrix contains stable, discreet microdroplets of the silicone fluids. The second method utilized to prepare such a fine dispersion is very-high-pressure injection of silicone into the aqueous phase. These microdroplets have been referred to as nanoparticles, but they are actually nanometer-sized fluid droplets as opposed to nanometer-sized sihcone resin particles, which are referred to by the same term (86). Both of the systems described above have been claimed to readily deposit onto hair and skin, and to increase ease of formulation (87,88). 

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