- Silicone-barium titanate composites with increased electromechanical sensitivity. the effects of the filler morphology
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A high molecular weight polydimethylsiloxane-α,ω-diol, synthesized in the lab, was used as a matrix for nanocomposites. Barium titanate nanoparticles, either cubic or nanorods, were obtained by a hydrothermal procedure and used as a filler. In order to ensure a good compatibility with the matrix, the filler was surface treated with a commercial surfactant. A highly reactive trifunctional silane was used as crosslinking agent in the presence of organometallic catalyst. Two other samples, the first consisting of pure crosslinked polydimethylsiloxane and the second being the polymer matrix filled with commercial barium titanate, were prepared and used as references to evaluate the influence of the presence of barium titanate nanoparticles and their shape on some characteristics of the resulting crosslinked composites: morphology, thermal behavior, moisture sorption, mechanical and dielectric characteristics. The electromechanical sensitivity and energy output were calculated on the basis of appropriate experimental data in order to estimate the potential of the composites for future electromechanical applications.
- Bele,Cazacu,Stiubianu,Vlad
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- Synthesis and structure of chiral silatranes derived from terpenes
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Starting with the chiral pool compounds (-)-menthone, (-)-limonene, (-)-β-pinene, and (-)-carvone, new homochiral triethanolamine derivatives were obtained and converted to chiral silatranes. These silatraries were characterized by crystal structure analyses and NMR techniques. Conformational analyses in the solid state and in solution show that the chiral terpene residues determine the direction of the ring puckering of the silatrane moiety.
- Wagner, Gabriele,Herrmann, Rudolf,Pedersen, Bj?rn,Scherer, Wolfgang
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- Preparation of acyloxysilanes
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Acyloxysilanes are prepared by the anhydrous reaction of stoichiometric amounts of a carboxylic acid with a mixture of a halosilane and a silazane in an aprotic solvent, such as diethyl ether, acetonitrile, tetrahydrofuran or toluene, in an inert gas atmosphere. In a preferred embodiment the silazane is prepared in situ by the reaction of the corresponding halosilane and ammonia. No catalyst is necessary and the reaction preferably is performed at a temperature of -5° C. to 45° C.
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- Process for the continuous preparation of acyloxysilanes
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Acyloxysilanes are prepared by a process of reacting an organochlorosilane with an excess of monocarboxylic anhydride at elevated temperature, thereby forming product acyloxysilane and by-product acyl chloride transferring the reaction mixture to the middle inlet of a separation tower having a still pot at its base, removing excess carboxylic anhydride by distillation at the tower top under reduced pressure, removing acyl chloride by-product from the separation tower, uniformly removing acyloxysilane from the tower still pot, and reacting virtually quantitatively the residual acid chloride present in the acyloxysilane removed from the still pot by adding a metal carboxylate to the acyloxysilane and separating the metal chlorides formed from the product.
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- Process for preparing triacetoxysilanes from tris(amino)silanes
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Triacetoxysilanes are prepared by adding a tris(amino)silane to acetic anhydride and maintaining the reaction mix at a temperature no greater than about 50° C.
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- Continuous process for preparing acyloxysilanes
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Acyloxysilanes are prepared by reacting a chlorosilane with an aliphatic carboxylic acid in a column at an elevated temperature and preferably at a pressure of about 760 mm Hg. wherein the aliphatic carboxylic acid in the vapor phase passes upward from the bottom of the column countercurrent to the flow of the chlorosilane passing downward in the column. The improvement comprises introducing the carboxylic acid into the column at such a rate that the carboxylic acid exceeds 1.3 moles per gram atom of silicon-bonded chlorine in the column and removing low boiling reaction by-products from the top of the column while collecting the acyloxysilane product dissolved in the aliphatic carboxylic acid at the bottom of the column. In a preferred embodiment, methyltriacetoxysilane is prepared by reacting methyltrichlorosilane with acetic acid in a heated fractionation column.
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