Polymers and Their Interactions with Hair

Cationic Polymers and Their Interactions with Hair 

Cationic polymers as a group are one of the more important types of polymers used in hair products. Because of their high degree of substan-tivity to hair, they are useful in shampoos and conditioners. Their major asset, high substantivity, is also a potential problem, because they can be so substantive that they are difficult to remove from hair with ordinary shampoos. 

Cationic ingredients in general are highly substantive to hair because of hair s low isoelectric point, which is approximately pH 3.67 [24] in cosmetically unaltered hair, and even lower in bleached hair. Therefore, at any pH above the isoelectric, the surface of hair bears a net negative charge, and positively charged (cationic) ingredients are attracted to it. 

Even monofunctional cationics are substantive to hair (i.e., they resist removal by water rinsing). For example, stearyl benzyl dimethyl ammonium chloride and cetyl trimethyl ammonium chloride are major active ingredients in creme rinse products because they are substantive to water rinsing of hair, and they condition the hair fiber surface. 

Dye staining tests [29, 30] show that substantivity of monofunctional cationics to water rinsing does not occur unless the hydrocarbon portion is approximately 8 to 10 carbon atoms. This effect occurs because, in addition to the electrostatic bond, sufficient Van der Waals attractive forces must exist to bind the molecule to the keratin in the presence of the aqueous phase. As the molecular size of the cationic structure is increased, even 

---

Creme rinses and most hair conditioners are basically compositions containing cationic surfactant in combination with long chain fatty alcohol or other lipid components. Distearyldimonium chloride, cetrimonium chloride, stearalkonium chloride, and behentrimonium methosulfate are typical cationic surfactants used in many of today s hair conditioning products. Amines like dimethyl stearamine or stearamidopropyl dimethylamine are other functional cationics used in these products. Cationic polymers such as Polyquaternium-10 (quaternized ceUulosic) and Polyquatemium-7 (copolymer of diallyl dimethyl ammonium chloride and acrylamide) are also used (more in shampoos than in hair conditioners) however, care must be taken to avoid buildup on hair when formulating with cationic polymers. See the section on Cationic Polymers and Their Interactions with Hair in Chapter 7. 

Cationic Polymers and Their Interactions with Hair 351... 

---