Trimethylsilane surfactants

Wagner, R., Wu, Y., Berlepsch, H.V., Zastrow, H., Weiland, B. and Perepelittchenko, L. (1999) Silicon-modified surfactants and wetting V. The spreading behaviour of trimethylsilane surfactants on energetically different solid surfaces. Appl. Organometallic Chem., 13( 11), 845-55. 

Wagner, R. andStrey, R. (1999) Phase behavior of binary water-trimethylsilane surfactant systems origin ofthe dilute lamellar phase. Langmuir, 15(4), 902-05. 

Analogous spreading experiments using the trimethylsilane surfactant B revealed quite a similar behavior (Fig. 27B). Again, the spreading area decreases with increasing concentration above 0.1 wt % when the experiment is performed at laboratory atmosphere, whereas it is exactly proportional to the amount of surfactant when spreading is carried out at 100% relative humidity. 

Halogeno silanes can be reacted readily with hydrides, e.g. magnesium hydride, in the presence of an ethereal solvent to give the appropriate hydrogen silane [4]. Applying this method e.g. trimethylsilane was obtained in excellent yields. Trimethylsilane was reacted with a-alkenols, allylglycidyl ether, and various alkenyl polyethers whereby the latter directly leads to a nonionic silane surfactant. The easy availability of trimethyl silane and its derivatives opens up a very interesting route to new Si-surfactants from the view of economy, too. 

Best surfactant behaviour was achieved in the case of the polyether trimethylsilane by introducing a hexyl spacer group in the molecule structure. For testing the wetting ability a droplet (50 pi) of an aqueous surfactant solution is applied by syringe to a clean sheet of polypropylene. Afterwards the increase of the diameter of the droplet is measured. The surface tension of the aqueous solution is usually determined by the well known ring method of du Nouy [5]. 

The combination of both the biodegradability and the stability towards hydrolysis is unique in the field of well known silicone surfactants and will ensure the widespread application of trimethylsilane based surfactants. Considering all these facts all applications for which trisiloxane surfactants are already used or at least recommended are opened up in general for the new silane surfactants. Furthermore, applications now can be taken into consideration for which the hydrolytically unstable trisiloxane derivatives failed in the past. 

The availability of trimethylsilane in larger amounts and reproducible quality was our key to silane surfactant chemistry [6]. The successful reduction of chlorotrimethylsilane with hydrides, such as magnesium hydride in etheral solution, gave the corresponding hydrogen silane in excellent yields. Further transformations with a,P-unsaturated olefins carrying a hydrophilic moiety opened up exciting new opportunities for the synthesis of Si-surfactants (Fig. 3) [7]. 

The Pt-catalyzed hydrosilylation of trimethyl silane and alkenols or alkenyl-polyethers lead to nonionic silane surfactants, whereas the addition of allylglycidyl ether to trimethylsilane results in a precursor for ionic derivatives. The epoxy group is highly reactive towards nucleophilic agents and can be easily transformed into quaternary ammonium, betaine, or sulfonate complexes. Additionally, cation-anion complexes can be formed by the transformation of two equivalents of epoxy silane with one equivalent of trialkyl ammonium hydrogen sulfite. The reaction of hydroxyalkyltrimethylsilane... 

By using a recently developed magnesium hydride technology, the trisiloxane lyophobic part in superspreading surfactants can be substituted by a trimethylsilane moiety. This synthetic route leads to both nonionic and ionic silane surfactants, which are hydrolytically stable even under extreme pH. Aqueous solutions of these new surfactants exhibit surface tension and wetting properties comparable to the traditional organomodified trisiloxane surfactants. The combination of hydrolytic stability and biodegradability offers chance for the widespread application of these silane based surfactants. 

The availability of trimethylsilane in larger amounts and reproducible quality by the reduction of chlorotrimethylsilane to trimethylsilane with magnesium hydride [91] in a milling reactor provided a better method in silane surfactant chemistry [92]. By using trimethylsilane in hydrosilylation reactions with a, 5-unsaturated compounds such as alkenols, allyl glycidyl ether, or alkenyl polyethers, a whole range of amphiphilic trimethylsilane compounds can be easily obtained (Fig. 8). 

The silane alcohol can serve as an intermediate for further reactions with sulfamic acid to give sulfates or EO leading to anionic or nonionic silane surfactants (Fig. 26), respectively. Alternatively, the nonionic derivatives can be obtained by hydrosilylation of the trimethylsilane with an alkenol polyether (Fig. 26). The hydrosilylation reaction with allyl glycidyl ether (Fig. 8)... 

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