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Siloxanolates

Early studies of the condensation reaction on the monomer level did not give the full picture of this process and only in the 1980s was polycondensation of siloxanols studied by using oligomeric model compounds (76,77). These studies revealed that in the presence of strong protic acids three processes must be considered linear condensation (eq. 14), cyclization (eq. 15), and disproportionation (eq. 16). [Pg.46]

Peroxides or other additives, eg, chlorinated paraffin, may also cause the thermoplastic resin to cross-link with the siloxanols. In this case, a tme interpenetrating polymer network forms, in which both phases are cross-linked. [Pg.74]

Performance of coupling agents in reinforced composites may depend as much on physical properties resulting from the method of appHcation as on the chemistry of the organofunctional silane. Physical solubiUty or compatibiUty of a siloxanol layer is determined by the nature and degree of siloxane condensation on a mineral surface. [Pg.74]

An interesting feature of the ring opening polymerization of siloxanes is their ability to proceed via either anionic or cationic mechanisms depending on the type of the catalyst employed. In the anionic polymerization alkali metal hydroxides, quaternary ammonium (I NOH) and phosphonium (R POH) bases and siloxanolates (Si—Oe M ) are the most widely used catalysts 1,2-4). They are usually employed at a level of 10 2 to KT4 weight percent depending on their activities and the reaction conditions. The activity of alkali metal hydroxides and siloxanolates decrease in the following order 76 79,126). [Pg.18]

In our own research, the functional termination of the living siloxanolate with a chlorosilane functional methacrylate leading to siloxane macromonomers with number average molecular weights from 1000 to 20,000 g/mole has been emphasized. Methacrylic and styrenic monomers were then copolymerized with these macromonomers to produce graft copolymers where the styrenic or acrylic monomers comprise the backbone, and the siloxane chains are pendant as grafts as depicted in Scheme 1. Copolymers were prepared with siloxane contents from 5 to 50 weight percent. [Pg.86]

An important method of preparing cyclic siloxanes and aminosiloxanes involves metallation of functionalized silanols, aminosilanols, or siloxanols followed by treatment with appropriate halosilanes. Intra- and intermolecular ring closure reactions are possible [10]. [Pg.52]

Siloxane compounds, in vitreous silica manufacture, 22 414 Siloxane materials, 20 240 Siloxane oligomers, in silicone polymerization, 22 555-556 Siloxanols, silylation and, 22 703 Silsesquioxane hybrids, 13 549 Silsesquioxanes, 15 188, 22 589-590 SilvaGas process, 3 696, 697 Silver (Ag), 22 636-667. See also Silver compounds. See Ag entries Argentothiosulfate complexes Batch desilverizing Lead-silver alloys Palladium-silver alloy membranes analytical methods for, 22 650-651 applications of, 22 636-637, 657-662 as bactericide, 22 656, 657, 660 barium alloys with, 3 344 in bimetallic monetary system, 22 647-648 in cast dental gold alloys, 8 307t coke formation on, 5 266 colloidal precipitation color, 7 343t colloidal suspensions, 7 275 color, 7 334, 335... [Pg.843]

A similar strategy was also applicable for the synthesis of six- and eight-membered siloxanol-ring systems. Hydrolysis of z-PrRSiCl2 (R = Ph, o-Tol) with ZnO and KOH provided the six-membered siloxane rings as a mixture of two constitutional isomers cis-trans-(i-PrRSiO)3 (539, R = Ph 540, R = o-Tol) and Wzr-(z-PrRSiO)3 (541, R = Ph 542, R = o-Tol) which were separated by preparative HPLC. Subsequent reaction with HC1/A1C13 and hydrolysis of the chloro intermediates yielded the same product for both isomers, namely Wzr-[z-Pr(OH)SiO]3 543, implying that isomerization occurs under these conditions (Scheme 75).484... [Pg.457]

Similarly, the controlled hydrolysis of TipSiCb 564 (Tip = 2,4,6-triisopropylphenyl) has afforded the products TipSi(OH)3 565, TipCl2SiOSiCl2Tip 566, and Tip(OH)2SiOSi(OH)2Tip 567. The condensation of 565-567 at different conditions has provided new discrete molecular siloxanols 568, 569, and 570, containing three to five Si atoms (Scheme 78).488... [Pg.458]

The self-organization of polysilanols in the presence of other hydrogen bond acceptors has been studied by several groups.512-516 Several other publications have dealt with the stepwise synthesis of siloxane and siloxanol chains.450,517-522 Recent work on fully condensed siloxane rings and silsesquioxane cages involves the non-aqueous hydrolysis of chlorosilanes - as well as mechanistic and structural studies. [Pg.458]

If the current ideas of APS surface interactions are to be supported, then the highly-oligomerized APS molecules must first revert to more reactive species such as silanol monomers. Perhaps the surface acts as its own acid/ base catalyst to break up the oligomerized fragments into monomers. The newly formed APS silanols are then free to form surface bonds and eventually a two-dimensional surface network [3]. Many experiments done in this laboratory and some discussed above are supportive of the labile nature of the siloxane bond. At or near the surface, this bond may be cleaved by water at elevated temperatures or at basic pH s, for instance, to form silanols or siloxanols. Subsequently, these molecules can react to form siloxanes and release the water molecule. [Pg.438]

Methylphenylcyclosiloxanes depolymerise under the influence of lithium siloxanolates and heating to form an equilibrium system ... [Pg.194]

Recently, sodium phenylsiloxanolate synthesis has been reported. For example, cyclo tetra siloxanolate [(Na ) C HjSi(0)0"] was synthesized by reacting tri-n-butoxyphenylsilane with sodium hydroxide in the presence of water [4], partial cage stracture [(Na )C HjSi(0(,5)20 ]3[C HjSi(0j 5)] was obtained that reacts with trimethoxy-phenylsilane and sodium hydroxide in the presence of water [5]. In 2003, we have... [Pg.205]

Mononuclear cyanide complexes also can be used as monodentate ligands to derivatize multinuclear metal assemblies. An example of this approach is the reaction between [Cu tpa)(CN)] + and the hexanuclear siloxanolate Cu 6[(PhSi02)6]2(w-BuOH)5 (220). The structure of the latter features six Cu... [Pg.234]

The rate of disappearance of the starting materials was followed as one approach to determine the effect of catalyst type and concentration on the rate of the ring-opening polymerization. Results are presented in this chapter for the potassium-siloxanolate-catalyzed system, as well as for the analogous tetramethylammonium- and tetrabutylphosphonium-siloxanolate-catalyzed systems. [Pg.146]

Materials. Octamethylcyclotetrasiloxane, D4, was generously supplied hy General Electric Company. l,3-Bis(3-aminopropyl)tetramethyldisiloxane (to be referred to subsequently as aminopropyldisiloxane) was obtained from Petrarch Systems, Inc. These materials were dried over calcium hydride and vacuum distilled prior to use. Potassium hydroxide, tetramethylammonium hydroxide pentahydrate, and tetrabutylphosphonium bromide used in the preparation of the siloxanolate catalysts were used as received from Aldrich. [Pg.147]

Catalyst Preparation. The potassium siloxanolate catalyst was prepared by charging finely crushed potassium hydroxide, D4, and toluene to a flask equipped with an overhead stirrer and an attached Dean-Stark trap with condenser. Argon was bubbled through the solution from below the level of the liquid to promote the elimination of water via a toluene azeotrope as the reaction proceeded. Typically, a D4/KOH molar ratio of 3 1 was used with enough toluene to form an approximately 50% (wt/vol) solution. The catalyst was allowed to form at 120 °C for 24 h, during which time the toluene-water mixture was eliminated and collected in the Dean-Stark trap. The clear catalyst was then diluted to an —35% (wt/vol) solution with dry toluene and stored in a desiccator until use. [Pg.147]

The tetramethylammonium siloxanolate catalyst was prepared similarly by charging tetramethylammonium hydroxide, D4, and an azeotropic agent to the flask and heating the reaction at 80 °C for 24 h. The lower reaction temperature was necessary to avoid decomposition of the ammonium catalyst. Under most conditions, this procedure produces an active catalyst that is not completely homogeneous. Although not precisely defined, some carbonate is known to be present in addition to the siloxanolate. [Pg.147]


See other pages where Siloxanolates is mentioned: [Pg.74]    [Pg.74]    [Pg.19]    [Pg.87]    [Pg.88]    [Pg.181]    [Pg.184]    [Pg.192]    [Pg.265]    [Pg.452]    [Pg.457]    [Pg.458]    [Pg.459]    [Pg.461]    [Pg.683]    [Pg.173]    [Pg.181]    [Pg.214]    [Pg.351]    [Pg.83]    [Pg.11]    [Pg.48]    [Pg.2230]    [Pg.65]    [Pg.123]    [Pg.74]    [Pg.74]    [Pg.145]   
See also in sourсe #XX -- [ Pg.339 ]




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Siloxanoles

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