Silicone surfactants preparation

Silicone surfactants are prepared using one of the following three routes ... 

The first silicone surfactants were prepared by reaction of alkoxy-functional silicones with hydroxyl terminated polyethers using the transetherification reaction [7] ... 

Silicone surfactants that are more hydrolytically stable are prepared by coupling polar groups to the silicone using hydrosilylation [14, 15] ... 

There is a considerable patent art concerning preparation of transparent mixtures of water with low molecular weight silicone oils using polymeric silicone surfactants. Some representative early references are Keil [47], Gee [48, 49], Gum [50] and Terae [51]. These compositions are called micro emulsions in the patents in the sense of being transparent mixtures of water, surfactant and oil - but note that they are transparent because of small particle size or because of index of refraction matching. 

No systematic studies of the use of silicone surfactants as emulsifiers have yet been published. Silicone polyoxyalkylene copolymers with relatively high molecular weight and a high proportion of silicone are effective water-in-silicone oil emulsifiers and a recent study of these copolymers suggests that they stabilize emulsions by a solid-particle mechanism [68]. This type of silicone surfactant has been used to prepare transparent water-in-oil emulsions (often with an active ingredient in the internal phase) for use as deodorants or antiperspirants as well as cosmetics and other personal care products. Their use as drug delivery vehicles has also been claimed. These copolymers can also be used to prepare multiple emulsions not requiring a two-pot process. 

The high hydrophobicity of silicones can complicate their use in some applications. For example, proteins can undergo denaturation in contact with silicones [1]. In such cases, the siloxane can be modified to include a hydrophilic domain. This is typically accomplished by functionalizing the silicone with a hydrophilic polymer such as poly(ethylene oxide)(PEO). Silicone surfactants of this type have found widespread use as stabilizers for polyurethane foams, and have been investigated as a structurant to prepare siloxane elastomers for biomaterials... 

Sorbitol Polyol-Modified Isocyanurate Foam (71). This foam was prepared according to the following procedure. Potassium 2-ethylhex-anoate containing 4% water was used as the catalyst (soluble in polyether polyols). 94 g of sorbitol-based polyether polyol having a hydroxyl number of 490, 8.5 g of the potassium 2-ethylhexanoate, 120 g of tris(chloroethyl) phosphate, 5 g of silicone surfactant, and 90 g of... 

A premix was prepared by blending the bisphenol A-epichloro-hydrin adduct, silicone surfactant and CFC-llA. Into the premix, polymeric isocyanate and the complex catalyst were added and the mixture was immediately agitated vigorously to produce a foamed material. The resulting foam had a density of 40 kg/m with fine cell structure. 

Component 2 was prepared by mixing 10 g of toluene, 1 g of silicone surfactant (Toray SH-193), and 7.6 g of hexamethylene diisocyanate. The two components were mixed in a container for 15 seconds. Rise time was 35 seconds, and the foam density was 0.042 g/cm. Aliphatic diisocyanates such as hydrogenated MDI and m-xylylene diisocyanate also act as effective activators, but aromatic isocyanates, such as MDI, TDI, were found not to be effective. 

The surfactants employed for polyurethane foams can be also used for preparing foamed composites. The surfactants include silicone surfactants, which consist of polysiloxane-polyoxyalkylene block-copolymers. 

The most widely used surfactants are copolymers based on dimethyl polysiloxane and polysiloxanes. Some of these silicones are prepared with ethylene and propylene oxides. Some silicones contain Si-... 

PU foams were prepared by the one-shot, free-rlse method. A homogeneous liquid mixture consisting of Nlax 31-28, Isonol-100, silicone surfactant DC-193 (Dow Corning), T-12, Nlax A-1 (Union Carbide), trlchlorofluoromethane (Freon llA, E.I. duPont de Nemours Co.), and water was mixed thoroughly with Isonate-143L. It was put Into a cold mold and allowed to free rise. 

SEM images show that silicone has filled and sealed the inter-monofilament pores and voids and indicates that the PEG silicone surfactants coating the fabrics were decomposed after plasma treadnent. The cleaved products coating the nylon fabric appear to be distributed very uniformly. This phenomenon is consistent with the results of the contact angle measuranents cleavage of the prepared surfactants leads to water-insoluble silanol moieties and two water-soluble products this process imparts excellent water repellency to the nylon fabric. Zhang et al. (2003) determined antibacterial properties qualitatively through measurements of areas from which S. aureus and K. pneumonia have been eradicated. The silicone coat at the eradicated area is not transparent. Biocidal treatments with both the silicone and PEG 2000 silicone surfactants improved the antibacterial properties of the nylon fabrics. The results we obtained before and alter plasma treatment were similar, especially for S. aureus. Thus, the sample treated with PEG 2000 silicone retained its antibacterial activity and water repellency after plasma treatment (Lin et al., 2006). 

Figure 11.4 Nitrogen adsorption-desorption isotherm for a silica film (designated as ZSU-38) prepared from mixtures of cationic and silicone surfactants. The materials were calcined at 500°C in air for 5 h. The corresponding BJH pore-size distribution...

Mesoporous silica with hexagonal order (designated as ZSU-4) was also prepared from mixtures of the silicone surfactants (Figure 11.1) and a PEO-PPO-PEO copolymer [33], as evidenced by electron microscopy and X-ray diffraction (see Figure 11.5). The calcined ZSU-4 gave a BET surface area of 841 m g". The BJH analysis of the isotherm (type IV with a large type-H 2 hysteresis loop) resulted in an average pore size of 8.1 run. 

The rates of thinning of vertically-supported, thin liquid films of polyol solutions of various silicone surfactants have been measured [37]. It was found that the rate for films stabilised by a trimethylsilyl-capped polysilicate (TCP a highly branched silicone not containing polyethers), was much lower than that for the films stabilised by common silicone polyether copolymer surfactants. The retardation of drainage rate was correlated with an increase in surface viscosity. Furthermore, it was noted that PU foams prepared using TCP were significantly more stable than those containing the commercial surfactants. 

Hydrolyzate is a major raw material from which other silicone compounds are prepared. Silicone derivatives can then be made using hydrolyzate or its various fractions. The unit operations used to fractionate, polymerize, and otherwise rehne hydrolyzate result in many commercially important compounds including silicone fluids, gums, cyclic compounds, silanol compounds, organofunc-tional silicone compounds, and silicone surfactants. 

The preferred polyesters are adipates, ethylene butylene adipate being favoured. The isocyanate used is MDI, and pure MDI rather than crude (mixed isomers) is found to give a product with best performance. The toxic risk from MDI is much lower than from TDI it is reduced further because it is contained in the quasi-prepolymer prepared by the chemical manufacturer and presents no appreciable health hazard at moulding. Chain extenders are usually low molecular weight glycols, with butane glycol being especially used. Other additives are silicone surfactants to improve cell structure, catalyst, a hydrolytic stabilizer, to prevent hydrolysis of the polyester, and colourant. 

The latest class of silicone surfactants to be prepared are the fluorosilicone copolymers (73,74). These compounds combine disiloxane or branched trisiloxane structures modified with fiuoroalkyl radicals as the hydrophobic moiety and polyethylene oxide units as the hydrophilic group. Two copolymers containing different fiuoroalkyl groups have been reported for use in shampoo systems. The materials containing 3,3,3, trifluoropropyl units were characterized by surface tensions approximately equivalent to dimethicone fluids ( 20.1 mN/m), while polymers containing 3,3,4,4,5,5,6,6,6, nonafluorohexyl groups displayed surface tensions as low as 17.6 mN/m (75). 

Silicone surfactants, sometimes referred to as organosilicones, are those with a poly(dimethyl siloxane) backbone. They are prepared by incorporation of a water-soluble or hydrophilic group into a siloxane backbone. The latter can also be... 

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