New amphoteric surfactants, dimethylaminoalkanesulfonates (DAMS), were synthesized by a ring opening reaction of alkylsultones, obtained by the reaction of α-olefin with sulfurtrioxide, with dimethylamine.
Judging from the results of
1H-NMR measurement, DAMS seemed to take a zwitterionic form in the region of pH<8 and an anionic one in the region of pH above 12. Results of ESR measurement using a spin probe, which is known to be capable of locating the inner part of micelle, showed smaller hyperfine splitting constant (a
N) in DAMS solution than those found in common surfactants, indicating that the micelle interior of DAMS has hydrophobic nature.
Surface activities of DAMS were increased with the decrease of distance between amino group and sulfonate group. On the contrary, Krafft points of 4-DAMS were lower than those of 3-DAMS. The solubilizing and emulsifying power of DAMS to nonpolar materials exceeded AOS and other amphoteric surfactants with corresponding alkyl chain length. DAMS also had a favorable lime soap dispersing power. Foamability of DAMS was similar to the common surfactants when it is applied to shampoo formulation. These performance of DAMS are considered to be due to zwitterionic form with hydrophobic nature under neutral or acidic condition.
Denaturing power to Bovine serum albumin, so called skin roughness, and primary skin irritation of DAMS were significantly lower than those found in conventional mild surfactants such as monoalkylphosphate and acyl glutamate.
In conclusion, DAMS is an advantageous amphoteric surfactant for cosmetics and toiletries having superior surface activities and practical performance as well as physicological mildness. Furthermore, DAMS has an economical benefit since it can be derived readily from solfonation product of α-olefin.
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