424
Langmuir 1993,9,424-430
Synthesis, Characterization, Stability, Aqueous Surface Activity, and Aqueous Solution Aggregation of the Novel, Cationic Siloxane Surfactants
(M~~S~O)~S~(M~)-(CH~)~+NM~~(CH~)ZOR X- (R = H, C(O)Me, C(O)NH(Ph);X = C1, Br, I, Nos, MeOSO3) Steven A. Snow Central Research and Development, Dow Corning Corporation, Mail Stop C042A1, Midland, Michigan 48686-0994 Received June 11, 1992. In Final Form: November 9,1992 This report describes the synthesis, characterization,stability, aqueous surface activity, and aqueous solution aggregation of the novel, cationic,siloxane surfactants (Me3Si0)zSi(Me)-(CH2)3+NMe~(CH2)20R X-(R = H, C(O)Me, C(O)NH(Ph); X = C1, Br, I, NO3, MeOSO3). The R = H, X = halide or MeOSOa The R = H, X = NO3 species are prepared by the methylationof (Me3SiO)2Si(Me)(CH2)3NMe(CH2)~0H. compound is prepared by the treatment of the R = H, X = I salt with &Nos. The R = C(O)Me,C(0)NH(Ph), X = NO3salts are synthesized by the reaction of the R = H, X = NO3 salt with either MeC(0)Cl [R = C(0)Me derivative] or (Ph)N--C=O [R = C(O)NH(Ph)derivative]. These compounds are shelf stable for up to a year but hydrolyze in aqueous solution at rates which are pH dependent. The purified products are highly effective aqueous surfactants, reducing the surface tension of water to 20-26 mN/m. For the R = H species, the effect of the counteranion on surface arealmolecule (A) and on the critical aggregation concentration (cac) follows the counteranion trend Me0503 < NO3 < Br < C1. Conversion of the R = H, X = NO3 species to R = C(O)Me,X = NO3results in an increase in cac and A. The behavior of the R = H, X = C1species (I)in aqueous NaCl solutionis differentthan that observed for the hydrocarbon surfactant cetyltrimethylammonium chloride (11). For I, A gradually increases as a function of [NaCl] up to 1 w t % NaCl, then it sharply decreases as a function of [NaCll at higher [NaClls. The cac of I decreases as [NaCll increases but does not scale linearly with the log of [NaCl]. For 11,both A and the cac linearly decrease with the log of [NaCll. This difference in behavior between I and I1 is not easily rationalized.
Introduction Recently we reported the synthesis and characterization of novel zwitterionic siloxane Surfactants.' These surfactants adsorb at the &/water interface, reducing the surface tension to approximately 21 mN/m. The utility of these surfactants as laundry foam boosting agents,2a and as organic surfactant additives,2bled to a search for less expensive and more efficient synthetic routes to these compounds. This study resulted in the discovery of a family of novel, cationic, quaternary ammonium salt functional, siloxane surfactants of the general formula (Me3SiO)zSi(Me)-(CH2)3+NMe2(CH2)zORX- (R = H, C(O)Me, C(O)NH(Ph); X = C1, Br, I, NO3, MeOS03). Early work on cationic siloxane surfactants was reported by Maki and co-workers? They prepared compounds of the formulas (MeaSiO)aSi-R, (Me3SiOSiMe2O)zSi(Me)R, and Me3Si(OSiMez),-R (R =: (CH&+NMe2R' C1-; R' = H, Me; n = 3, 4). These species reduced the surface tension of water to 22-23 mN/m with critical micelle concentrations (cmc's)of 0.1-1.0 wt % . These surfactants were stable in aqueous solution in the pH range of 4.5-10. Outside that pH range, surface activity was rapidly lost. These characteristics are similar to those we observed for zwitterionic siloxane surfactants.l Recently Schmaucks and co-workers reported the synthesis, characterization, aqueous surface activity, and micelle formation of the species Me3SiO(SiMe20),-
SiR1R2(CH2)3+NMe2R3X-(Rl, R2 = Me, Me3SiO; n = 0, 1;R3= alkyl or alkenyl; X = hal~gen).~ These compounds also decreased the surface tension of water to the range of 18-26.5 mN/M. Many of these surfactants were excellent aqueous wetting agents on paraffin. The wide range of applications for cationic, quaternary ammonium salt functional siloxanes is apparent by the patents that have issued. Reid reported the synthesis and aqueoussurfaceactivityof cationic siloxanesof the formula (M~~S~O)~S~(M~)-(CH&OCHOCH(OH)CH~+NM~~R C1(R = H, Me).Sa These compounds reduced the surface tension of water to 21 mN/m at 1.0 wt % concentration and were claimed to impart corrosion protection to metal surfaces. Rosen and Prokai reported fire-fighting foam formulationscontainingcationicsiloxanesurfactanta such as (Me3SiO)2Si(Me)-(CH2)3+NEt3 I-." Yetter reported that cyclic siloxane polymers containing quaternary ammonium salt linkages, such as [MeSi(O)-(CH2)2+N(Me)2(C12H2s)lnnBr-, displayed surface activity and were useful as bactericides and anticariogenic agents.sc Ziemelis and Roth reported that polysiloxanes containing pendant groups such as -(CH2)3+NH(CH2)2NH&Hd(phenyl) C1strongly adsorbed on proteinaceous surfaces such as skin and hair." The utility of organofunctional, polyalkylsiloxanes,containing both quaternary ammonium functional and polyether functional groups, of the general formula Me3siO(SiM~),(Mesi(l)O)m(MeSiR(2)0) Me (R(1) = -(CHS)OCH&H(OH)CH~+NM~~ CH3C 0-; R(2) =
(1) (a) Snow, S.A.; Fenton, W. N.; Owen, M. J. Langmuir 1990,6,385. (b) Snow, S. A.; Fenton, W. N.; Owen, M. J. Langmuir 1991, 7,868. (2)(a) Lo,S.J.;Snow, S. A. U.S. Patent 4,879,051(1989). (b) Petroff, L. J. U.S.Patent 4,784,799(1988). (3)Maki, H.; Horiguchi, Y.;Suga, T.; Komori, S. Yukagaku 1970,19 (ll),1029.
(4) Schmaucke, G.;Sonnek, 0.; Wustneck, R.; Herbst, M.;Ra",M. Lan#muir 1992.8. __. _ _ __, _1724 -. , - _.
0743-7463/93/2409-0424$04.#/0
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(5) (a)Reid,W.G.U.S.Patent3,389,160(1966). (b)Rosen,M.;Prokai, B. US.Patent 3,677,347(1972). (c)Yetter,J.U.S.Patent 3,624,12O(1971). (d)Ziemelie, M.; Roth, C. U.S. Patent 4,472,566(1964). (e) Haq,Z.UK Patent Application, GB 2,201,433A (1988).
8 1993 American Chemical Society
Cationic Siloxane Surfactants
Langmuir, Vol. 9, No.2, 1993 426
Table I. Elemental Analysis of Silicone Surfactants* ~ ( C ~ H ~ O ) ~ ~ ( C Z as H fabric ~O)Z conditioning H) agents,was recently disclosed by Haq." %C %H %N This paper describes the synthesis, characterization, compound" anal. calcd anal. calcd anal. calcd stability, aqueous surface activity, and solution intermoMOH+Cl42.2 43.3 10.6 9.8 3.6 3.8 lecular aggregation of the novel, cationic, siloxane species MOH+Br39.5 38.9 11.0 10.3 3.3 3.2 (M~~S~O)~S~(M~)(CHZ)~+NM~Z(CHZ)ZOR X- (R = H, MOH+I35.1 35.2 7.5 7.9 2.9 3.0 C(O)Me,C(O)NH(Ph);X = C1, Br, I, Nos, MeOSOs).For MOH+MeOS0339.5 38.9 9.5 9.2 3.2 3.0 the R = H species above, it was quickly recognized that MOH+N0340.6 38.8 9.2 9.5 6.8 6.6 the presence of both a quaternary ammonium functional 42.1 41.3 MOC(O)Me+N038.8 8.7 6.1 5.8 MOC(O)NH(Ph)+N03- 47.3 46.7 8.1 9.8 7.9 7.8 group and a hydroxyl group might allow for exceptionally efficient adsorption of the surfactant to anionic, hydroxM = (Me&iO)zSi(Me)- (CHz)3NMe&Hz)z-. * Slightimpurities ylated surfaces such as cotton-containing fabrics or silica. account for the observed minimal deviations from calculatedamounts. The presence of the siloxane hydrophobe would result in an unique modification of these surfaces. Indeed, the icals and used as received. The purity of the CTAC was confirmed by analysis of the plot of aqueous surface tension versus log adsorption of these surfactants onto cotton/polyester concentration CTAC. The plot was linear up to the cmc value, towelsresulted in significant fabricsoftening and antistatic and the cmc (extrapolated from the break point in the plot) was effects.6 1.27 mol/L at 23 OC, which compared favorably to the The technological utility of surfactants usually stems literature value of 1.3 (10-3) mol/L at 30 0C.8 No minimum was from their efficient adsorption at various interfaces and/ detected in the plot above the cmc. Reagent grade sodium or their formation of aggregated structures in solutionsuch chloride was purchased from Fisher Scientific and dried in vacuo as micelles, vesicles, and liquid crystals. The surface prior to use. activity and solution aggregation properties of these new 11. Surfactant Synthesis. (a) (MeJSiO)zSi(Me)-(CHZ)Jcationic siloxane Surfactants can potentially be controlled C1. C12Si(Me)-(CH2)&1, prepared by the hydrosilylation of allyl by (1)forming select chemical derivatives of the hydroxyl chloride with ClzSi(Me)H,was received from an internal source at Dow Corning Corp. This chemical is also commercially group, (2) varying the counterion, and (3) adding various available from Hula America Inc. It was purified by fractional salts to the solutions. Toward this goal of the control of distillation (bp 98 OC/18 mmHg). The chlorosilane was then solution surfactant properties, these studies are directed mixed with a &fold molar excess of (Me3Si)zO and 2 wt % of toward understanding the effect of these variables on Filtrol acid clay (Harshaw Chemical). After 30 min, the mixture aqueous surface activity (adsorption at the aidwater was heated to 60 OC for an hour. Gas chromatographic analysis interfaceand surface tension reduction)and solutionphase of this mixture indicated essentially quantitative conversion of intermolecular aggregation such as micellization. ClzSi(Me)-(CHZ)&l into (MeaSiO)zSi(Me)-(CHz)aCl. The re-
Experimental Section I. Surfactant Characterization a n d Surface Tension Measurements. Proton ('H) nuclear magnetic resonance (NMR) spectra were acquired on either a Varian T-60 or Varian X200 NMR spectrometer. NMR samples were prepared in 5 mm 0.d. tubes in the presence of deuterated solvents. Chemical shifts were referenced to tetramethylsilane. Infrared spectra were acquired on a Beckmann 4240 spectrometer. Samples were mulled into Nujol for the spectral acquisition. Elemental analyses were obtained from the Analytical Research Department at Dow Coming Corp. Aqueous equilibrium surface tensions were obtained by the DuNuoy ring method using a Cahn electrobalance.' Appropriate correction factors were applied to the balance measurements. Surfactant solutionswere prepared with distilled,deionized water. Sample temperatures were stable to f0.2 OC. Prior to measurements on surfactant solutions, the surface tension of the distilled, deionized water was measured. These water values were in the range of 71.9 f 0.3 mN/m. Samples were aged 15min prior to the surface tension measurement. The DuNuoy ring was withdrawn 15-60 s after initial sample contact. To assure that the measurements were not being overtly affected by the possible hydrolysis of the surfactants, the surface tensions of dilute (
