Synthesis and Surface Properties of CO2H Type Gemini Surfactant Having Semifluoroalkyl Group as Hydrophobic Group

Abstract

Abstract Novel CO2H type gemini surfactants having semifluoroalkyl group (Rf-(CH2)n-: Rf = C4F9, C6F13, C8F17 and n = 2, 3) as hydrophobic group were successfully synthesized and their surface properties were studied. (Perfluoroalkyl)ethylmalonic esters were synthesized by the reaction of malonic ester with Rf(CH2)2I using NaH as base in THF/DMF. (Perfluoroalkyl)propylmalonic esters were synthesized from allylmalonic ester, namely by the radical addition of Rf-I using AIBN as initiator, and reduction with Zn/AcOH. Those fluoroalkylated malonic esters were connected using Br(CH2)sBr (s = 3, 4) to give dimeric tetraesters. Then, tetraesters were hydrolyzed using KOH/EtOH followed by decarboxylation in AcOH to afford CO2H type gemini surfactants. To study their surface properties, both surface tension-concentration and surface pressure-area isotherms were measured. As expected, COOH geminis showed one order of magnitude lower critical micellar concentrations (CMC) than that of conventional 1+1 type surfactant. In the surface pressure-area measurements, as length of fluoroalkyl increased, lift-off area (AL) decreased, monolayers were clearly formed upon compression and the limited areas (A∞) for C6F13 and C8F17 were smaller than twice of that of C8F17(CH2)2COOH. Especially, COOH geminis having Rf = C8F17 and -(CH2)3- spacer showed the formation of solid phase monolayers, and the planar five membered ring-like structure was proposed.