Silanes

<p>Alkyl Silane - Dipodal Surface Bonding<br>Aliphatic, fluorinated aliphatic or substituted aromatic hydrocarbon substituents are the hydrophobic entities which enable silanes to induce surface hydrophobicity. The organic substitution of the silane must be non-polar. The hydrophobic effect of the organic substitution can be related to the free energy of transfer of hydrocarbon molecules from an aqueous phase to a homogeneous hydrocarbon phase. A successful hydrophobic coating must eliminate or mitigate hydrogen bonding and shield polar surfaces from interaction with water by creating a non-polar interphase. Although silane and silicone derived coatings are in general the most hydrophobic, they maintain a high degree of permeability to water vapor. This allows coatings to breathe and reduce deterioration at the coating interface associated with entrapped water. Since ions are not transported through non-polar silane and silicone coatings, they offer protection to composite structures ranging from pigmented coatings to rebar reinforced concrete. A selection guide for hydrophobic silanes can be found on pages 22-31 of the Hydrophobicity, Hydrophilicity and Silane Surface Modification brochure.<br>Non Functional Alkoxy Silane<br>Silane coupling agents have the ability to form a durable bond between organic and inorganic materials to generate desired heterogeneous environments or to incorporate the bulk properties of different phases into a uniform composite structure. The general formula has two classes of functionality. The hydrolyzable group forms stable condensation products with siliceous surfaces and other oxides such as those of aluminum, zirconium, tin, titanium, and nickel. The organofunctional group alters the wetting or adhesion characteristics of the substrate, utilizes the substrate to catalyze chemical transformations at the heterogeneous interface, orders the interfacial region, or modifies its partition characteristics, and significantly effects the covalent bond between organic and inorganic materials.<br>Dipodal Silane<br>Dipodal silanes are a series of adhesion promoters that have intrinsic hydrolytic stabilities up to ~10,000 times greater than conventional silanes and are used in applications such as plastic optics, multilayer printed circuit boards and as adhesive primers for ferrous and nonferrous metals. They have the ability to form up to six bonds to a substrate compared to conventional silanes with the ability to form only three bonds to a substrate. Many conventional coupling agents are frequently used in combination with 10-40% of a non-functional dipodal silane, where the conventional coupling agent provides the appropriate functionality for the application, and the non-functional dipodal silane provides increased durability. Also known as bis-silanes additives enhance hydrolytic stability, which impacts on increased product shelf life, ensures better substrate bonding and also leads to improved mechanical properties in coatings as well as composite applications.<br>1,8-Bis(triethoxysilyl)octane; 4,4,13,13-Tetraethoxy-3,14-dioxa-4,13-disilahexadecane<br>Employed in sol-gel synthesis of mesoporous structuresCrosslinker for moisture-cure silicone RTVs with improved environmental resistanceSol-gels of α,ω-bis(trialkoxysilyl)alkanes reported<br></p>

<p>Tri-substituted Silane Reducing Agent<br>Organosilanes are hydrocarbon-like and possess the ability to serve as both ionic and free-radical reducing agents. These reagents and their reaction by-products are safer and more easily handled and disposed than many other reducing agents. The metallic nature of silicon and its low electronegativity relative to hydrogen lead to polarization of the Si-H bond yielding a hydridic hydrogen and a milder reducing agent compared to aluminum-, boron-, and other metal-based hydrides. A summary of some key silane reductions are presented in Table 1 of the Silicon-Based Reducing Agents brochure.<br>Methyldichlorosilane; Dichloromethylsilane<br>Viscosity: 0.60 cStΔHcomb: 163 kJ/molΔHvap: 29.3 kJ/molDipole moment: 1.91 debyeCoefficient of thermal expansion: 1.0 x 10-3Specific heat: 0.8 J/g/°CVapor pressure, 24 °C: 400 mmCritical temperature: 215-8 °CCritical pressure: 37.7 atmProvides better diastereoselective reductive aldol reaction between an aldehyde and an acrylate ester than other silanesForms high-boiling polymeric by-products upon aqueous work-upExtensive review of silicon based reducing agents: Larson, G.; Fry, J. L. "Ionic and Organometallic-Catalyzed Organosilane Reductions", Wipf, P., Ed.; Wiley, 2007<br></p>

<p>Ester Functional Trialkoxy Silane<br>Silane coupling agents have the ability to form a durable bond between organic and inorganic materials to generate desired heterogeneous environments or to incorporate the bulk properties of different phases into a uniform composite structure. The general formula has two classes of functionality. The hydrolyzable group forms stable condensation products with siliceous surfaces and other oxides such as those of aluminum, zirconium, tin, titanium, and nickel. The organofunctional group alters the wetting or adhesion characteristics of the substrate, utilizes the substrate to catalyze chemical transformations at the heterogeneous interface, orders the interfacial region, or modifies its partition characteristics, and significantly effects the covalent bond between organic and inorganic materials.<br>Hydrophilic Silane - Polar - Hydrogen Bonding<br>Aliphatic, fluorinated aliphatic or substituted aromatic hydrocarbon substituents are the hydrophobic entities which enable silanes to induce surface hydrophobicity. The organic substitution of the silane must be non-polar. The hydrophobic effect of the organic substitution can be related to the free energy of transfer of hydrocarbon molecules from an aqueous phase to a homogeneous hydrocarbon phase. A successful hydrophobic coating must eliminate or mitigate hydrogen bonding and shield polar surfaces from interaction with water by creating a non-polar interphase. Although silane and silicone derived coatings are in general the most hydrophobic, they maintain a high degree of permeability to water vapor. This allows coatings to breathe and reduce deterioration at the coating interface associated with entrapped water. Since ions are not transported through non-polar silane and silicone coatings, they offer protection to composite structures ranging from pigmented coatings to rebar reinforced concrete. A selection guide for hydrophobic silanes can be found on pages 22-31 of the Hydrophobicity, Hydrophilicity and Silane Surface Modification brochure.<br>Acetoxymethyltriethoxysilane; (Triethoxysilylmethyl)acetate<br>Hydrolyzes to form stable silanol solutions in neutral water<br></p>

<p>(3-Trimethoxysilyl)propyl 2-bromo-2-methylpropionate<br>Halogen functional trialkoxy silaneUsed for surface initiated atom-transfer radical-polymerization, ATRPUsed in microparticle surface modification<br></p>

<p>3-Aminopropyldimethylethoxysilane, 3-(dimethylethoxysilyl)propylamine<br>Monoamino functional trialkoxy silanePrimary amine coupling agent for UV cure and epoxy systemsUsed in DNA array technology and microparticle surface modificationΔHform: 147.6 kcal/mol<br></p>

<p>2-(4-Pyridylethyl)triethoxysilane, 4-(triethoxysilyl)pyridine<br>Monoamino functional trialkoxy silaneAmber liquidForms self-assembled layers which can be “nano-shaved” by scanning AFMUsed in microparticle surface modification<br></p>

<p>Azide Functional Trialkoxy Silane<br>Silane coupling agents have the ability to form a durable bond between organic and inorganic materials to generate desired heterogeneous environments or to incorporate the bulk properties of different phases into a uniform composite structure. The general formula has two classes of functionality. The hydrolyzable group forms stable condensation products with siliceous surfaces and other oxides such as those of aluminum, zirconium, tin, titanium, and nickel. The organofunctional group alters the wetting or adhesion characteristics of the substrate, utilizes the substrate to catalyze chemical transformations at the heterogeneous interface, orders the interfacial region, or modifies its partition characteristics, and significantly effects the covalent bond between organic and inorganic materials.<br>3-Azidopropyltriethoxysilane; Trimethoxysilylpropylazide<br>Used with click chemistry to introduce and immobilize discrete complexes onto the SBA-15 surfaceUsed in the preparation of poly-L-lysine bound to silica nanoparticlesCoupling agent for surface modificationAVOID CONTACT WITH METALS<br></p>

<p>Alkenylsilane Cross-Coupling Agent<br>The cross-coupling reaction is a highly useful methodology for the formation of carbon-carbon bonds. It involves two reagents, with one typically being a suitable organometallic reagent - the nucleophile - and the other a suitable organic substrate, normally an unsaturated halide, tosylate or similar - the electrophile.<br>p-(t-Butyldimethylsiloxy)styrene; p-Vinyl-t-Butyldimethylbenzene<br>Useful for Heck cross-coupling to substituted protectedhydroxy functional styrenesUndergoes radical and anionic polymerizationExtensive review of silicon based cross-coupling agents: Denmark, S. E. et al. "Organic Reactions, Volume 75" Denmark, S. E. ed., John Wiley and Sons, 233, 2011<br></p>

<p>ALD Material<br>Atomic layer deposition (ALD) is a chemically self-limiting deposition technique that is based on the sequential use of a gaseous chemical process. A thin film (as fine as -0.1 Å per cycle) results from repeating the deposition sequence as many times as needed to reach a certain thickness. The major characteristic of the films is the resulting conformality and the controlled deposition manner. Precursor selection is key in ALD processes, namely finding molecules which will have enough reactivity to produce the desired films yet are stable enough to be handled and safely delivered to the reaction chamber.<br>Tetrachlorosilane; Silicon chloride; Silicon tetrachloride<br>Viscosity: 0.35 cStΔHform: -640 kJ/molΔHvap: 31.8 kJ/molΔHfus: 45.2 J/gSurface tension: 19.7 mN/mDielectric constant: 2.40Vapor pressure, 20 °C: 194 mmCritical pressure: 37.0 atmCritical temperature: 234 °CCoefficient of thermal expansion: 1.1 x 10-3Specific heat: 0.84 J/g/°Reaction with living alkali metal terminated polymers results in star polymersPrimary industrial use - combustion with hydrogen and air to give fumed silicaEnantioselectively opens stilbine epoxides to trichlorosilylated chlorohydrinsPromotes the reaction of aldehydes with isocyanides<br></p>