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j. Cosmet. Sci., 51, 91-101 (March/April 2000) Structure-function relationships of dimethicone copolyol NELSON E. PRIETO and ANTHONY J. O'LENICK, Petroj•rm Inc., Fernandina Beach, FL (N.E.P.), and Siltech USA, Dacula, GA (A.J. O'L.). Accepted for publication January 31, 2000. INTRODUCTION Throughout the 1990s dimethicone copolyol (DMC) surfactants and their derivatives have been an important and growing class of surface-active agents. These materials are used in a diverse area of applications such as cosmetics, textiles, coatings, lubricants, and detergents, due to their ability to provide maximum surface-active properties in a cost-effective manner (1-3). Despite the growing use of these silicone-based compounds, studies regarding the basic understanding of the effect of their structure on surfactant properties remain limited, relative to the information openly available for organic sur- factants. The present study was undertaken to determine the effect of DMC structure on its surfactant properties. Properties studied included wetting, cloud point, critical micelie concentration (cmc), foaming, solubility, spreading, emulsification, and ocular irritation. The relationship of the results to application is discussed. DIMETHICONE COPOLYOL CHEMISTRY The term dimethicone copolyol has been adopted by the Cosmetics, Toiletry and Fra- grance Association to describe a class of silicone/polyoxyalkylene derivatives. DMC surfactants are a class of compounds that conform to the following general structure: CH 3 CH 3 CH 3 CH 3 CH3-Si--(-O--Si--)•--(O--Si)b--O--Si--CH 3 CH 3 CH 3 (CH2) 3 CH 3 I O-(CH2CH20)x-(CH2CH(CH3)O)yH The nomenclature was developed to reflect the fact that the molecule is (a) a silicone polymer (dimethicone), (b) a copolymer ("copoly" part), and (c) hydroxyl functional ("o1" 91