CATIONIC QUATERNARY COMPOUNDS 269 NV T P1X P•X BIX B•X 11 lO 9 8 7 6 5 4 2 1 o NV T P1X P2X B1X B2X Figure 6. The effect of condition and cysteic acid content of hair on stearalkonium chloride and laurdi- monium hydrolyzed wheat protein sorption (NV = normal virgin hair T = tinted hair P IX, 2X -- one-time, two-time permed hair B1 X, 2X = one-time, two-time bleached hair). bleach. Other indications of hair damage may be obtained from the measurement of cysteic acid content which, in a study of the effects of reactive chemical processes on hair, was shown to be pronounced at the cuticle layer of the hair (17). Two examples are displayed in Figure 6: uptake of stearalkonium chloride and laurdimonium hydrolyzed wheat protein at various hair conditions. As the hair became more damaged (increase of wt% cysteic acid), the amount of cationic compounds adsorbed to hair increased. This phenomenon has been well recognized (11,13,19). By the same token, hair with oxi- dative damage adsorbs cationic compounds more readily than hair with reductive dam- age. The results suggest a phenomenon in which the cationic ammonium compounds are

270 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS attracted by the anionic sulfonate group of the cysteic acid at the outer layer of the hair fiber. Relative comparison of the substantivity of the cationic compounds can also be made on the basis of their equivalent weight. Quaternary molecules having higher equivalent weight exhibit better substantivity. In the present study, an apparent equivalent weight of the compounds tested can be readily calculated from the calibration curves (Figure 2) by the following equation: Equiv wt (mg/mequiv) = slope x Ns•)s where slope = slope of the appropriate calibration curve (mls•)s/mg cationic compound) Ns•)s = normality of SDS titrant (0.01 mequiv/ml) Table II shows the calculated equivalent weights obtained from the potentiometric titration method under the tested conditions. These values may not represent the "true" equivalent weight of the cationic compounds since their titration is based on the assumption of a complete 1:1 ion pair interaction. For example, the calculated value for stearalkonium chloride is 357 mg/mequiv whereas the theoretical value is 423 mg/ mequiv. Among other factors, titratable impurities in the commercial grade samples are possibly accountable for such a discrepancy. Table II also shows the quantitative uptake of the quaternary compounds by bleached hair that was treated at 35øC for 30 minutes with a 0.05% solution of the cationic compound. The calculated equivalent weights display an order of stearalkonium chloride • cocodimonium hydrolyzed keratin protein quaternium-26 laurdimonium hy- drolyzed wheat protein polyquaternium-4. This trend is similar to the order of the substantivity of these compounds to hair, i.e., stearalkonium chloride • cocodimonium hydrolyzed keratin protein quaternium-26 laurdimonium hydrolyzed wheat pro- tein. Polyquaternium-4, having the highest equivalent weight, displays the lowest substantivity. This anomaly is not well understood. However, the high rate of increase in substantivity of polyquaternium-4 at higher concentration and longer treatment time is noted (Figures 3,4). Thus, even though a standardized method for the study of the Table II Comparison of the Calculated Equivalent Weight and the Substantivity of Tested Compounds Material Calculated Substantivity using equivalent weight 0.05% solution (mg/mequiv) (mg/0.1 g hair) Stearalkonium chloride Cocodimonium hydrolyzed keratin protein Quaternium-26 Laurdimonium hydrolyzed wheat protein Polyquaternium-4 357 8.65 37O 8.43 526 9.25 714 10.09 833 4.62