Novel Fluorinated Gemini Surfactants with γ-Butyrolactone Segments

Abstract

In this work, novel γ-butyrolactone-type monomeric and dimeric (gemini) surfactants with a semifluoroalkyl group [Rf– (CH₂)₃–; Rf = C₄F₉, C₆F₁₃, C₈F₁₇] as the hydrophobic group were successfully synthesized. Dimethyl malonate was dimerized or connected using Br(CH₂)_sBr (s = 0, 1, 2, 3) to give tetraesters, and they were bis-allylated. Radical addition of fluoroalkyl using Rf–I and an initiator, i.e., 2,2’-azobisisobutyronitrile for C₄F₉ or di-t-butyl peroxide for C₆F₁₃ and C₈F₁₇, was perform at high temperature, with prolonged heating, to obtain bis(semifluoroalkyl)-dilactone diesters. These dilactone diesters were hydrolyzed using KOH/EtOH followed by decarboxylation in AcOH to afford γ-butyrolactonetype gemini surfactants. Common 1 + 1 semifluoroalkyl lactone surfactants were synthesized using the same method. Their surfactant properties [critical micelle concentration (CMC), γ_CMC, pC₂₀, Γ_CMC, and A_G] were investigated by measuring the surface tension of the γ-hydroxybutyrate form prepared in aqueous tetrabutylammonium hydroxide solution. As expected, the CMC values of the gemini surfactants were more than one order of magnitude smaller than those of the corresponding 1 + 1 surfactants. Other properties also showed the excellent ability of the gemini structure to reduce the surface tension. These surfactants were easily and quantitatively recovered by acidification. The monomeric surfactant was recovered in the γ-hydroxybutyric acid form, and the gemini surfactant as a mixture of γ-butyrolactone and γ-hydroxybutyric acid forms.