Heterofunctional condensation

Examples of organooxasilacycloalkanes have been presented by Makarova and co-workers.43 2,8-Dichloro-2,4,4,6,6,8,10,10,12,12-decamethyl-5-carbacyclohexasiloxane, 4,7-dichloro-2,2,4,7-tetramethyl-l,3-dioxa-2,4,7-trisila-cycloheptane, and 4,8-dichloro-2,2,4,8-tetramethyl-l,3-dioxa-2,4,8-trisilacyclooctane were prepared for the first time by the heterofunctional condensation of l,l,7,7-tetrachloro-l,3,3,5,5,7-hexamethyl-4-carbatetrasiloxane with... 

The reaction is a complex process involving substitution reactions and/or homo-and heterofunctional condensations (Scheme 2). 

The second stage consists of the heterofunctional condensation of a, -dihydroxydiphenylsiloxane obtained at the first stage with triacetoxy-methylsilane ... 

The production of silicon tetrachloride (Fig. 46) comprises the following main stages the condensation of dihydroxydiphenylsilane and water distillation the heterofunctional condensation of the product of stage I with tri-acetoxymethylsilane the flushing of the obtained product with water and the distillation of the solvent. 

The reaction of heterofunctional condensation is carried out in reactor 5, which is a steel enameled apparatus with a water vapour jacket and an anchor agitator. Reactor 5 is loaded at a residual pressure of 730 200 GPa with a,eo-dihydroxydiphenylsiloxane, the product of dihydroxydiphenylsilane condensation a calculated amount of the toluene solution of triace-toxymethylsilane self-flows at agitationffom batch box 6. 

The separation of toluene from the product of heterofunctional condensation is carried out in two stages. First, toluene is distilled at atmospheric pressure to 50% of the volume of the reactive mixture then, the mixture is "clarified" (purified from traces of moisture) by settling at 80-100 °C for 1-2 hours. The settled water is poured off through the bottom drain of reactor 5 into collector 7 the product in the reactor is heated to 100-120 °C. At this temperature and a residual pressure of 730 200 GPa toluene is further distilled until the content of volatile substances is less than 3%. The va-... 

The reaction of equation 14 probably occurs stepwise, and it is a complex process involving substitution reactions and/or homo- and heterofunctional condensations. Numerous cyclodi-, tri- and tetrasilazanes (76) are obtained in the reactions of aminofluorosilanes (74) with lithium organyls via thermal LiF elimination of lithium aminofluorosilane derivatives (75) (equation 18)69-75. The primary products of such condensations in the reaction of fluorosilanes with lithium amide have been synthesized in order to study the mechanisms of their formation. An (R2SiFNLiH) compound was characterized by X-ray diffraction8,76 77. 

The present section discusses investigation results of the basic regularities and mechanisms of dihydroxyorganocyclosiloxanes interaction with dihydroxy(dichloro, dihydride)organocyclosiloxa-nes, clears up synthetic abilities of homo- and heterofunctional condensation in the field of syn-thesizing cyclolinear oligomers, and considers surveys of thermal and other physical and chemical properties of synthesized oligomers. 

Monomers containing the corresponding fragment R are introduced into the reaction at the stage of heterofunctional condensation. 

Excellent reviews summarize the established preparative procedures for a great many organoboroxines " . Versatile preparative methods include heterofunctional condensation, which occurs readily at RT ... 

Organodichlorosiloxyorgano-cyclotri(tetra-penta)siloxanes have been prepared by heterofunctional condensation of hydroxyorganocyclotri(tetra-penta)-siloxanes with organotrichlorosilanes in the presence of amines. The hydrosilylation of methylvinyltetra-phenyltrisiloxane with methyldichlorosilane in the presence of platinum chlorohydric acid leads to dichloroorganosilacarbocyclotrisiloxane. The composition and structure of difunctional organocyclosiloxanes was determined by elementary and functional analysis, molecular mass determination, IR, NMR ( H, C) and mass spectral data. 

The heterofunctional condensation of dichlororganosiloxycyclotri(tetra-penta)siloxanes and dichlororganosililcarbocyclotrisiloxane with dihydroxydimethylsiloxanes in the presence of pyridine has been investigated. It was shown that for short lengths of the linear dimethylsiloxane link (n < 4), the reaction of heterofunctional condensation proceeds both intermolecularly with formation of copolymers and intramolecularly with formation of bicycloorganosiloxanes. 

Synthesis of Organosiloxane Copolymers with Monocyclic Fragments in the Side Chain by Heterofunctional Condensation... 

Alkoxysilane silanol condensation reactions play an important role in sol-gel technology, the manufacture of silicone resins, the vulcanization of silicones and in surface modiflcation by alkoxysilanes. There have been recent investigations by Chojnowski and coworkers into the kinetics of acid-catalysed heterofunctional condensation of model alkoxy and silanol functional siloxanes. The heterofunctional reaction involving SiOEt and SiOH competes with the homofunctional reaction of SiOH with SiOH. The rates of each process are similar, but are influenced by the medium and hence by the concentration of the reactants. Hydrolysis of the ethoxysiloxane as well as ethanolysis of the silanol groups leads to extensive interconversion of functional groups. These interconversion processes are two orders of magnitude faster than those of the condensation reactions. 

Other publications have also appeared describing condensation kinetics with heterogeneous catalysts by a designed experimental approach to optimize reaction conditions, stannous octanoate condensation catalysis and the role of bifunctional catalysis mechanisms. A bifunctional transition state , shown for compound 8, was postulated to explain the kinetics of heterofunctional condensation reactions catalysed by CI3CCOOH, Et2NOH, MeEtC=NOH or CH3COOH (equation 6). 

Synthesis of a new modification of silica soluble in THF is described. At the first synthetic step, a hyperbranched polyethoxysiloxane (HBPES) is synthesized by heterofunctional condensation using triethoxysilanol previously generated in reaction mixture by neutralization of correspondent sodium salt with acetic acid. At this step, the process was monitored by IR spectroscopy, SEC, and Si NMR spectroscopy. At the second step, hydrolysis and intramolecular condensation involving silanol groups is carried out to yield silica sol macromolecules. A SAXS method was used to determine the size and fractal coefficient of trimethylsilated derivatives and silica sols obtained. An atomic-force microscopy imaging of silica sol supported on a mica substrate showed the silica sol particles to be predominantly spherical in shape. Prospects for theoretical, experimental and practical applications of silica sols are discussed. 

Synthesis of the hyperbranched poiyethoxysiloxane. Viewed from a standpoint of the chemistry of dendrimers and hyperbranched polymers, triethoxysilanol (regarded in (20) as a primary product of hydrolysis) is no more than a reactant AB3 according to the Flory condition. This signifies that, by generating this product under the conditions of a heterofunctional condensation, one can direct the reaction such that a hyperbranched poiyethoxysiloxane is formed, that is, to make the process structurally selective. It is known that, in hyperbranched polymers, cyclization is a minor contributor to the molecular structuring because of the paucity of A-type functionalities. In other words, with allowance made for structural imperfection of the hyperbranched polymer and for the fact that proportions of the dentritic, linear and end chains depend on a number of factors, it is possible in principle to obtain an end product with desired properties by monitoring structure, rather than process parameters, of the polymer formed. 

Rate constants and activation energies are reported from a kinetic study of the heterofunctional condensation of hydroxydimethylsilyl-m-carbaborane with RSiMcgCl (R=Me, Pr, CF3CH2CH2, CHgCl, or H), which proceeds by a mechanism close to Ss2. The reaction centre is equally sensitive to the induction and steric effects of the substituent R. ... 

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