876 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS O, o ' i& ' 260 ' ' 4ao MOLECULAR WEIGHT xlO -3 Figure 17. Curl retention after 30 minutes exposure at 90% RH vs. molecular weight of poly- vinyl pyrrolidone, 0.06 g of resin deposited per hair swatch (22øC) Figure 18. • 50' a: 4C z 0 io 20 30 40 50 60 MOLE(%) HYDROXYL CONTENT Curl retention after 30 minutes exposure at 90% RH vs. hydroxyl functionality (mole %) of copolymers, 0.06 g deposited (22øC) copolymer are illustrated in Figs. 19 and 20. Tensile strength (psi) at 90% RH tends to decrease with increased neutralization, while elongation increases. These observations appear to be consistent with the reported changes in film hardness as the neutralization varies. Whereas unneutralized films are stronger and more brittle with higher Sward values, the films become weaker and softer as neutralization is increased. A summary of commercial hair spray polymer properties is presented in Table I. Polymer B, not a commercial polymer, is included to illustrate the improved properties that may be achieved by polymer design. The data included in the table clearly show the relationship of curl retention and polymer properties at elevated humidity.

POLYMER PROPERTIES INFLUENCING CURL RETENTION 877 Figure 19. 80O 600 400 200 0 2b 46 6b 8b •oo NEUTRALIZATION (%) Tensile strength (psi) at 90% RH rs. neutralization with AMPD for Polymer A (2•øC) Table I Polymer Properties of Commercial Resins at 9070 Relative Humidity Polymer Mean Curl Equilibrium Moisture Vapor Retention Moisture Transmission Sward (%) Content Rate (my/ Rocker Tensile 180 Min (%) cm2/sec/cm) Hardness (psi) Polymer B (unneut) 63 1.5 2.6 16 1000 Polymer B (60% neut) 54 6 3.0 10 400 Polymer A • (60% neut) 49 9 3.4 4 360 Polymer A (100% neut) 46 14 3.8 0 230 DMHF 34 13 6.1 0 30 PVP/VA 33 38 4.7 0 200 PVP 28 45 6.9 0 200 • RESYN 28-1310, National Starch and Chemical Corp., Plainfield, N.J. The resins are listed in order of decreasing curl retention. The correlation coefficients for a linear fit of curl retention vs. polymer properties are' Equilibrium moisture content .......................... --0.86 Moisture vapor transmission ........................... --0.93 Sward Rocker hardness ............. '•. :-. ............... 0.88 Tensile strength ...................................... 0.84 The anomalous relationship of the moisture absorption and curl retention for DMHF can be clarified by observing the high moisture