Syntheses and properties of hydrolysis resistant twin-tail trisiloxane surfactants

Abstract

To improve the hydrolysis resistant ability (HRA) and spreading ability (SA) of trisiloxane surfactants, twin-tail trisiloxane surfactants of the general formula RNRCH 2CH(OH)CH 2(OCH 2CH 2) x OCH 3 (R = Me 3SiOSiMe(CH 2) 3OSiMe 3; x = 8.4, 12.9, 17.5, 22) have been synthesized by reacting single-tail trisiloxane surfactants with 3-chloropropyltrisiloxane. Their structures were characterized with proton nuclear magnetic resonance ( 1H NMR) and carbon nuclear magnetic resonance ( 13C NMR). The surface activity and hydrolysis resistant properties of the trisiloxane surfactants prepared have also been studied. All of the twin-tail trisiloxane surfactants reduce the surface tension of water to less than 23 mN/m at concentration levels of 10 −5 mol/L and 10 −4 mol/L. The SA of the twin-tail trisiloxane surfactant solution on low-energy solid surface is better than that of the corresponding single-tail trisiloxane surfactant. For the twin-tail trisiloxane surfactants containing average ethoxy units of 12.9, the best spreading ability is found. It is suggested that the shape of hydrophobic group, the molar ratio of methyl to methylene in the hydrophobic group and the hydrophile/lipophile balance (HLB) of trisiloxane surfactants are able to impact their SA. The surface tension values of aqueous solutions (0.1 wt%) of the twin-tail trisiloxane surfactants containing ethoxy units of 8.4, 12.9 and 17.5, are still less than 21 mN/m over 270 days in neutral environment. The HRA of the twin-tail trisiloxane surfactants is obviously superior to that of single-tail trisiloxane analogue surfactants and increases with the decrease of the number of ethoxy units.