32 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS TABLE 3--COMPARISON OF D•STEAR•NS 1,3 (6) 1,2 (9) Form M.P., øC. L.S., fk. Form M.P.,ø C. L. S., _ Beta-a 77.7' 50.2 Alpha 59.5 54.5 Beta-b 78.2 52.8 Beta primer 71 48.3 * Dielectric Measurements (3b). t Altered nomenclature. The absence of alpha for 1,3-distearin is the most unusual feature and may be associated with the symmetry of the molecule. The basis for the occurrence of two beta-like forms is not clear, but their separateness of identity is certain. SATURATED MONOGLYCERIDES The saturated 1-monoglycerides normally occur almost to the exclusion of 2-monoglycerides, the equilibrium ratio being about 9:1 (10). Here, too, the crystallization behavior of the isomers is notably different (Table 4). The monomorphism and lack of an alpha form for 2-monostearin is again associated with symmetry of the molecule. With 1-monostearin there is a reversible alpha ,•- sub-alpha transforma- tion and a stable beta form which crystallizes from polar solvents in beauti- TABLE 4--COMPARISON OF MONOSTEARINS (6) , 1-Mono . - -2-Mono , Thermal Pt., Form øC. L.S., •. Form M.P., øC. L.S., -•. Sub-alpha 49 50.3 Alpha 74 50.2 Beta prime 78 50.1 Beta 81.5 50.1 Form I 74.5 43.8 ful platelets. Beta prime appears out of solvent only. The small long- spacing of alpha (smaller than calculated for a fully extended molecule) suggests a tilted alpha form, although alpha typically has chains perpen- dicular to the plane of molecular ends. Monoglycerides, with two free hydroxyl groups per molecule, are of particular interest because of their surface active properties. Phase study normally sheds no light on these properties except in a negative way the greater the proportion of emulsifier which is in the solid phase the less are its hydroxyl groups available for emulsification, but the behavior is not simple. Whatever their mode of action, solid emulsifiers such as monostearin (glyceryl monostearate) have been found to be highly desirable in some cosmetic preparations. Phase study, including x-ray diffraction, gives in- formation on the "consistency potential" of an emulsifier, not on the

THE POLYMORPHISM OF GL¾CERIDES 33 stiffening arising from any emulsification per se, but rather on the stiffening due to the network of solid crystallites. The typical monostearate of commerce is a mixture of mono-, di-, and triglycerides, and the information of Table 4 on 1-monostearin cannot be applied without discrimination. The data would pertain somewhat more directly to, e.g., Myverol 1805, a product of high monostearin content. DISATURATED TRIOLYCERIDES Disaturated triglycerides melt sufficiently high that they may be of in- terest as solid components of cosmetics. Cacao butter which is about 75 per cent disaturated (the remainder being mainly monosaturated) is fre- TABLE 5---COMPARISONS OF 2- AND I-OLEYLDISTEARIN (11) ..... 2-Oleyldistearin , - 1-Oleyldistearin - Form M.P., øC. L .S., •. Form M.P., øC. L. S., •k. Alpha-3 22.4 80 Alph a-3 30.4 80 (Beta prime*-3 35 68) Beta Prime-3 43.5 70.8 Sub-beta-3 36.2 73 Beta-3 44.3 64 * From solvent only. quently used. The range in type of solidification behavior of disaturated glycerides is suggested by the accompanying Table 5 for oleyldistearins. All forms of both glycerides have triple-chain-length structures, i.e., there is a segregation of saturated from unsaturated chains (6). There is a greater spread in m.p. between the lowest and highest melting forms of 2-oleyl- distearin than between those of the isomer. Stable forms are of beta and beta prime type, respectively. Discussion There are, in the glyceride family, solid compounds which show a wide variety of solidification behavior--different levels of melting, different de- grees of supercooling, most of them with only irreversible but some with re- versible transformations. There are compounds with different stiffening powers associated with different crystal habits. And there is a range from the entirely nonemulsifying solid triglycerides to the strongly surface-active solid monoglycerides. The information which has been tabulated for various glyceride types is only a beginning toward the preparation and control of cosmetic prepara- tions involving such materials, but the importance of mastery of the be- havior of possible components of a system cannot be over-emphasized in formulation problems. And as has been said, many of the types of solidifi- cation behavior exhibited by the various glycerides are also found among other solidifying cosmetic materials and the same tools which have been