Amino-siloxane

FIGURE 9.33 Analysis of cationic poly(amino siloxane). Columns PSS PFG 100 + 1000. Eluent HFIP + O.l A1 KtFat. Temp 25°C. Detection UV 230 nm, Rl. Calibration PSS PDMS siloxane standards. 

The stability of the aminosilanolate salts explains the position of substituents. For example, in reactions with halosilanes, numerous mono-, bis-, tris- and tetrakis-l-amino-siloxanes are formed [7-10],e. g ... 

The tetrakis-(l-amino-siloxane) condenses thermally, yielding a spirocyclic six-membered ring... 

Starting with the 1-amino-siloxanes, further substitutions turn out to be more complicated. Lithium salts of these compoimds form, depending on the properties and bulkiness of the silyl groups, 1,3-disilazane-l-olates or the less stable l-amido-l,3-disiloxanes. The first case includes a 1,3-silyl group migration from the oxygen to the nitrogen atom. 

Lithium salts of amino-siloxanes react with fluorosilanes to give in the absence of strong steric or electronic restraints, the isomeric silylamino-l,3-disiloxane. A l,3-(0—>N)-silyl group migration has occurred. The analogous raction with difluorosilanes leads to both isomers, and with trifluorosilanes no isomerization or silyl group migration is observed. 

Cosolvents ana Surfactants Many nonvolatile polar substances cannot be dissolved at moderate temperatures in nonpolar fluids such as CO9. Cosolvents (also called entrainers, modifiers, moderators) such as alcohols and acetone have been added to fluids to raise the solvent strength. The addition of only 2 mol % of the complexing agent tri-/i-butyl phosphate (TBP) to CO9 increases the solubility ofnydro-quinone by a factor of 250 due to Lewis acid-base interactions. Veiy recently, surfac tants have been used to form reverse micelles, microemulsions, and polymeric latexes in SCFs including CO9. These organized molecular assemblies can dissolve hydrophilic solutes and ionic species such as amino acids and even proteins. Examples of surfactant tails which interact favorably with CO9 include fluoroethers, fluoroacrylates, fluoroalkanes, propylene oxides, and siloxanes. 

Silane coupling agents may contribute hydrophilic properties to the interface, especially when amino functional silanes, such as epoxies and urethane silanes, are used as primers for reactive polymers. The primer may supply much more amine functionality than can possibly react with the resin at the interphase. Those amines that could not react are hydrophilic and, therefore, responsible for the poor water resistance of bonds. An effective way to use hydrophilic silanes is to blend them with hydrophobic silanes such as phenyltrimethoxysilane. Mixed siloxane primers also have an improved thermal stability, which is typical for aromatic silicones [42]. 

Organofunctional siloxane oligomers, amino-propyl-terminated 15, 25, 26, 37, 38... 

A variety of reactions have been conducted. Catalysts based on noble metals on Deloxan amino poly siloxane supports have been used. Hitzler et al. (1998) have reported alkylation of mesitylene with propylene or wopropanol in SC propylene or CO2 using a solid acid Deloxan catalyst. Pesiri et al. (1998) have carried out selective epoxidation in SC CO2 with transition metal catalysts (V, Ti, Mo) and tert-BHPO high conversion and selectivity have been reported. 

Barboiu, M., Guizard, C., Luca, C., Albu, B., Hovnanian, N. and Palmeri, J. (1999) A new alternative to amino add transport Facilitated transport of L-phenylalanine by hybrid siloxane membrane containing a fixed site macrocydic complexant. Journal of Membrane Science, 161, 193-206. 

A wide range of additives can also be introduced into the sol-gel matrices in order to modulate the hydrophobicity of the materials and to improve enzyme stability, activity and accessibility, leading to hybrid or even composite sol-gel matrices. Polymers [157,179,180] such as polyethyleneglycol, polyvinylpyrrolidone, polyvinylalcohol, polyglycidol, polyethyleneimine, polyacrylate have been simultaneously entrapped with enzymes in a siloxane matrix, as well as organic additives (sugar, amino add)... 

Matisons, J. G. Provatas, A. Synthesis and Characterization of Amino Acid Functional Siloxanes. In Silicones and Silicone-Modified Materials-, Clarson, S. J., Fitzgerald, J. J., Owen, M. J., Smith, S. D., Eds. AGS Symposium Series 729 American Chemical Society Washington, DC, 2000 pp 128-163. 

The compounds I and II represent intermediates for the synthesis of either carboxy functional or amino functional polysiloxanes. To this end I or II is either saponified with sodium hydroxide and concomitantly polycon-densated to a poly(carboxylaIky1 methyl siloxane) (III) or reduced to an amino alkyl methyl dialkoxy silane with sodium borohydride (J 5). ... 

Artificial skin had been made from a bilayer fabricated from a cross-linked mixture of bovine hide, collagen, and chondroitin-B-sulfate derived from shark cartilage with a thin top layer of siloxane. The siloxane layer acts as a moisture- and oxygen-permeable support and to protect the lower layer from the outer world allowing skin formation to occur in conjunction with the lower layer. Poly(amino acid) films have also been used as an artificial skin. Research continues in search of a skin that can be effectively used to cover extensive wounds and for burn patients. 

Copolymerizations between pairs of cyclic esters, acetals, sulfides, siloxanes, alkenes, lactams, lactones, /V-carboxy-a-amino acid anhydrides, imines, and other cyclic monomers... 

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