Polymers play several roles in the coloring of hair. They act as thickeners for oxidation dyes. In this role polymers include a range of associative thickeners (anionic, cationic, amphoteric, nonionic, and hydrophobically modifi ed alkali swellable) as well as hydrophobically modifi d ethoxylated urethanes. Alkylmethicones and aminosilicones play a role in color retention. Non-associative thickeners help in achieving hair lightening.
This article surveys patents and technical literature, principally from the past 10 years, to report advances in polymers for hair coloring.
Oxidation dyes are made up of dye precursors (such as ortho- and paraphenylenediamine, or ortho- and paraamino phenols). The dye precursors are colorless compounds that can penetrate the hair fi ber and in the presence of oxidizing agent, they condense to become colored compounds. The color can be modifi ed by including “couplers” such as meta-phenylenediamine.
The oxidation dye compositions are usually thickened to localize the dye action on the hair and to prevent the dye composition from flowing down the face and into the eyes. Originally, thickeners such as carbomers, hydroxyethylcellulose, or low HLB surfactants were used. The structure of carbomers consists of microgels of cross-linked poly(acrylic acid), whereas hydroxyethylcellulose thickens by entanglement of the relatively rigidbackboned cellulose macromolecules. It has been reported that oxidation dye compositions thickened with these traditional thickeners result in a dull shade on the hair and as a result, high concentrations of dyes are required to obtain intense colors.