HYDROPHILICALLY MODIFIED SILICONE ELASTOMERS 195 precursor polymer so that the number of reactive silicon hydride sites was constant for all of the elastomer samples that were made. In this situation, a trade-off exists between the degree of PEG substitution and the crosslink density since the crosslinker and the allyloxy-terminated PEG both consume the silicon hydride groups on the precursor polymer. So, for a given level of PEG substitution, there is a maximum crosslink density that can be achieved for that PEG-DCP. In practice, however, we have found that various processing parameters affect the extent of the crosslinking reaction so that crosslink density can be varied somewhat independently for a particular level of PEG substitution. The level of PEG substitution is obviously an important factor for determining the properties of a particular PEG-DCP since it will determine the overall hydrophilicity of the elastomer. However, we have found that the crosslink density is also quite important. When the crosslink density is low, the PEG-DCP has a more extended configuration and behaves more like a liquid. When the crosslink density is high, the PEG-DCP has more elastomeric character and behaves more like the unmodified DCP elastomer. EXPERIMENTAL METHODS WATER-UPTAKE TEST The sample of PEG-DCP was diluted with cyclopentasiloxane to produce a dispersion of 9% elastomer in cyclopentasiloxane (emulsions of selected samples were also made with more dilute dispersions). Water was slowly added with a pipette, a drop at a time, to the elastomer dispersion, while mixing at about 300-400 rpm until the emulsion would no longer accept additional drops of water. The endpoint was determined by carefully observing whether or not the drop was incorporated into the emulsion. If there was some doubt, the mixer was stopped and the emulsion was examined to determine if there were droplets of free water in the emulsion. If free water was not observed immediately, then the emulsion was checked again after 24 hours for water separation. If there was water separation, the test was repeated using a fresh sample, and the water addition was stopped short of the previous endpoint and the sample was observed again for water separation. By repeating the test several times, the precise endpoint can be determined. Mixing was accomplished by stirring with a combination of two mixing blades spaced approximately 1.5 inches apart on the same shaft. The mixer was a Lightnin model L1U08. The lower mixing blade was a 1.5-inch-diameter high-shear radial-flow impeller (Lightnin R-100), and the upper blade was a four-lobe pitched impeller (Lightnin A-200). The repeatability of this test was determined to be +/-1%, based on repeated testing of blinded duplicate samples. ANTIPERSPIRANT GEL FORMULA AND PROCEDURE Ingredient Weight (%) Silicone phase Aqueous phase PEG-DCP (15 % dispersed in cyclopentasiloxane) 6.7' Cyclopentasiloxane 10.3 ACH-303** 62.5 Deionized water 8.9 Propylene glycol 11.6 * Equivalent to 1% PEG-DCP on a 100% solids basis. When dimethicone copolyol was used, 1% of this emulsifier was used and the amount of cyclopentasiloxane was adjusted to keep the amount of silicone phase the same as for the formulas with PEG-DCP. ** 50% aqueous solution of aluminum chlorohydrate (supplied by Summit Research).

196 JOURNAL OF COSMETIC SCIENCE Procedure. The aqueous and silicone phases were blended in separate containers until they were homogeneous. The aqueous phase was then added to the silicone phase while mixing with the same Lightnin mixer and stirrer configuration described for the water- uptake test. The mixer speed was set at 1376 rpm, and after all the water phase was added, mixing was continued for ten minutes. Anhydrous Roll-On Antiperspirant Ingredient Weight (%) DCP (12.5% in cyclopentasiloxane) Bentone gel VS 5* REZAL 36G powder** Cyclopentasiloxane Variable Variable 22.0 q.s. to 100% * A blend of Quaternium-18 Hectorite, cyclomethicone, and SD alcohol 40 (supplied by Elementis Specialties). ** Aluminum-zirconium tetrachlorohydrex-GLY powder (supplied by Reheis, Incorporated). ANHYDROUS ANTIPERSPIRANT FORMULAS AND PROCEDURE Procedure. All of the ingredients were weighed into a glass beaker and mixed using a kitchen hand-held mixer (Braun Handblender, model MR 360) for approximately one minute. Anhydrous Soft Solid Antiperspirant Ingredient Weight (%) Elastomer (DCP or PEG-DCP) Variable AZG-370* 25.0 Cyclopentasiloxane q.s. to 100% * Aluminum-zirconium tetrachlorohydrex-GLY powder (supplied by Summit Research). Procedure. All of the ingredients were weighed into a glass beaker and mixed using the same laboratory mixer and stirrer configuration described for the water-uptake test. The mixer was stopped periodically so that the sides of the beaker could be scraped down to ensure that the formula was uniformly mixed. MULTIPLE EMULSION FORMULA AND PROCEDURE Ingredient Weight (%) Part A PEG-DCP (12% in cyclopentasiloxane) 5.7 Cyclopentasiloxane 12.4 Tocopherol acetate 1.0 Part B Deionized water 45.8 Magnesium sulfate 2.1 P.art C Laureth-7 3.0 Part D Deionized water 28.7 Magnesium sulfate 1.3