Silicone surfactants Synthesis

The synthesis of organosilicones and organosilicone surfactants has been well described elsewhere [36-39] and hence only a brief review is given here. Industrially the manufacture of silicones is performed stepwise via the alkylchlorosilanes, produced through the reaction of elemental silicon with methyl chloride (the Muller—Rochow Process) [40,41]. Inclusion of HC1 and/or H2(g) into the reaction mixture, as in Eq. (1.2), yields CH3HSiCl2, the precursor to the organofunctional silanes, and therefore the silicone surfactants ... 

The use of surfactant self-assembly in the synthesis of mesoporous materials has become a very active field of research in the last two decades. However, the literature on the use of silicone surfactants in that field is still scarce. 

FIG. 8 Synthesis of ionic silicone surfactants from epoxy functional siloxanes. 

Inverse structures have been published for use in polyurethane foam formation [43]. Monofunctional siloxane chains are attached to a multifunctional polyether backbone. However, significant advantages over classical silicone surfactant structures could not demonstrated. A major drawback of this approach is the difficult synthesis of monofunctional siloxanes. 

Folk S. L., DeSimone J. M., and Samulski E. T., Cationic poly(dimethylsiloxane) surfactants Synthesis, characterization, and aggregation behavior in dense carbon dioxide, fluori-nated, and silicon-containing solvents. Polymer 2001,42, 231-232. 

Huan, K. Bes, L. Haddleton, D. M. Khoshdel, E. Surfactant Properties of Poly(dimethylsiloxane)-Gontaining Block Copolymers from Living Radical Polymerization. In Synthesis and Properties of Silicones and Silicone-Modified Materials Clarson, S. J., Fitzgerald, J. J., Owen, M. J., Smith, S. D., Van Dyke, M. E., Eds. ACS Symposium Series 838 American Chemical Society Washington, DC, 2003 pp 260-272. 

Silica Nanoparticles. The base-catalyzed hydrolysis of silicon aikoxides in microemulsions produces nanoparticles (20-39). Aqueous ammonia has been used primarily as the base, with AOT and nonionic polyoxyethylene ethers as the main surfactants. Figure 2.2.6 presents a flow diagram for the synthesis of pure silica (23-32) the microemulsion is first prepared and then the alkoxide is added. As can be seen from Table 2.2.1, the microemulsions include the systems AOT/ isooctane/water/ammonia, AOT/toluene/water/ammonia, NP-5/cyclohexane/water/ ammonia, and NP-4/heptane/water/ammonia. Typical reaction times are l -5 days. Various modified silica nanoparticles have also been prepared, including hydropho-... 

Our synthesis is based on the hydrolysis of a silicon alkoxide (TEOS Si(OCH2CH3)4) in a diluted solution of nonionic polyethylene oxide-based surfactants. The hydrolysis is then induced by the addition of a small amount of sodium fluoride [5], Depending on the initial mixing conditions, the size of the solubilized objects leads to either a colorless or milky emulsion. Small particles ( 300 nm) with a 3D worm-hole porous structure or small hollow spheres with mesoporous walls, are usually obtained [6]. The synthesis we report herein after exhibits an apparently slight but actually drastic change in the preparation conditions. The main feature of this approach is an intermediate step that utilizes a mild acidity (pH 2 - 4), in which, prior to the reaction, a stable colorless microemulsion containing all reactants is... 

Synthesis of MCM-41 with Additives. The hydrothermal crystallization procedure as described earlier [10] was modified by adding additional salts like tetraalkylammonium (TAA+) bromide or alkali bromides to the synthesis gel [11]. Sodium silicate solution ( 14% NaOH, 27% Si02) was used as the silicon source. Cetyltrimethylammonium (CTA) bromide was used as the surfactant (Cl6). Other surfactants like octadecylltrimethylammonium (ODA) bromide (C,8), myristyltrimethylammonium (MTA) bromide (C,4) were also used to get MCM-41 structures with different pore diameter. Different tetralkylammonium or alkali halide salts were dissolved in little water and added to the gel before addition of the silica source. The final gel mixture was stirred for 2 h at room temperature and then transferred into polypropylene bottles and statically heated at 100°C for 4 days under autogeneous pressure. The final solid material obtained was washed with plenty of water, dried and calcined (heating rate l°C/min) at 560°C for 6 h. 

Chemical Thermodynamics Mesoporous Materials, Synthesis and Properties Micelles Silicone (Siloxane) Surfactants... 

In this review, we addressed the synthesis of well-defined monodimensional sugar-grafted polysiloxanes. For this reason, we excluded from this paper the synthesis of silicones (poly)-glycosides as surfactants, obtained by glycosylation of hydroxyl-terminated polysiloxanes and the preparation of polysaccharide-silicone adducts. Both are essentially described in patents, from which straighforward data concerning the sttucture of the products and the outcome of the reactions are difficult to extract. For silicone glycosides, some descriptions can be found, only in patents, for example in US 5,428,142 [2]. They are usually prepared by a Fischer... 

The synthesis of MCM-41 was extended into very wide reaction conditions and various reactants. The silicon resource may be either organic silicon compounds (e.g., TEOS, TMOS, TBOS) or inorganic compounds (such as amorphous silica, soluble silicate). Synthesis temperature can be from lower than room temperature to high temperature 150 °C). Reaction time may vary from several minutes to a few weeks. The synthesis media can be from very basic to near neutral. The long-chain quaternary ammonium (C TMA) surfactant is the best template. 

Many of the non-silica compositions showed problems with the stability and quality of the structure. Efforts to address these issues have been on going and quite successful in some cases such as all-alumina compositions (see below). Silica-based materials remain dominant as the most versatile and best quality molecular sieves (structure and stability) available by a facile synthesis. These attributes, especially the convenient synthesis made mesoporous silicate attractive for post-synthesis functionalization with other elements as well as organic moieties with active groups/ccnters. Recently the compositional diversity has been extended further to include both silica and organic moieties within the framework. The new class is referred to as periodic mesoporous organosilicas (PMOs). The synthesis involves surfactant-assisted assembly by hydrolysis of organo-silicon compounds. Additional discussion of the PMOs is presented below. 

Synthesis of organized mesoporous aluminas is based on the same approaches as those successfully used for the synthesis of mesoporous molecular sieves ( anionic , cationic , and neutral ) using aluminum alkoxide as the source of aluminum and in the absence of any silicon source. In contrast to the synthesis of siliceous MCM-41, the cationic route to organized mesoporous aluminas using hexadecyltrimethylammonium cations is the least applied and understood. Cabrera et al. [68] described the possibility to tailor the pore dimensions from 3.3 to 6.0 nm by modifying the ratio of surfactant, water and triethanolamine however, this synthesis route seems to be less reproducible compared with anionic and neutral routes. 

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