Cyclosiloxanes synthesis

In the above cyclosiloxane synthesis sufficient solvent is added during catalytic equilibration to favor cyclic formation. After equilibrium is established, the catalyst is neutralized or removed, and the oligomeric products isolated by distillation or crystallization. 

We found as the most convenient method for the cyclosiloxane synthesis the cyclocondensation of the chlorodisilanes with the siloxanediols or the disilanediol in conditions following the dilution principle using pyridine as HCl acceptor. 

Backer, M. W. Pernisz, U. C. Photoexcitation and Photoemission Spectra of Phenyl-Substituted Cyclosiloxanes. In Synthesis and Properties of Silicones and Silicone-Modified Materials Clarson, S. J., Fitzgerald, J. J., Owen, M. J., Smith, S. D., Van Dyke, M. E., Eds. ACS Symposium Series 838 American Chemical Society Washington, DC, 2003 pp 105-116. 

The sequential addition method also allows the synthesis of many different block copolymers in which the two monomers have different functional groups, such as epoxide with lactone, lactide or cyclic anhydride, cyclic ether with 2-methyl-2-oxazoline, imine or episul-Hde, lactone with lactide or cyclic carbonate, cycloalkene with acetylene, and ferrocenophane with cyclosiloxane [Aida et al., 1985 Barakat et al., 2001 Dreyfuss and Dreyfuss, 1989 Farren et al., 1989 Inoue and Aida, 1989 Keul et al., 1988 Kobayashi et al., 1990a,b,c Massey et al., 1998 Yasuda et al., 1984]. 

The synthesis of higher order comb or star polymers with more than 20 PIB arms emanating from a core of condensed siloxanes, preferably cyclosiloxanes has been described (15). 

Sormani PM, McGrath JE (1985) Kinetics and mechanisms of the anionic ring opening polymerization of cyclosiloxanes in the presence of bis(l,3-aminopropyl tetramethyl-disiloxane) In McGrath JE (ed) Ring opening polymerization kinetics mechanisms and synthesis. ACS Symposium Series No 286... 

The present state of the synthesis of sihcon organic oligomers and polymers of beadshaped struc-ture is reviewed by condensation techniques, but not by polymerization or exchange polymerization, because in the latter cases, primary siloxane procurements may not be preserved due to instability of =Si-0-Si= bond in cyclosiloxanes. 

If desired, the linear oligosiloxanes, and indeed any linear polydimethylsiloxane, can be converted into cyclosiloxanes by base-catalyzed pyrolysis. If this reaction is carried out under equilibrating conditions and the products are fractionally distilled with removal only of the most volatile compound, D3, the entire mixture can be converted to this valuable intermediate. This procedure is frequently used to obtain pure D3 and D4, useful for polymer synthesis by ring-opening polymerization. 

With the purpose of increasing the range of available block copolymers, comonomers other than methacrylates and acrylates can also be involved in sequential polymerization, provided that they are susceptible to anionic polymerization. Dienes, styrene derivatives, vinylpyridines , oxiranes and cyclosiloxanes are examples of such comonomers. The order of the sequential addition is, however, of critical importance for the synthesis to be successful. Indeed, the pX a of the conjugated acid of the living chain-end of the first block must be at least equal to or even larger than that of the second monomer. Translated to a nucleophilicity scale, this pK effect results in the following order of reactivity dienes styrenes > vinylpyridines > methacrylates and acrylates > oxiranes > siloxanes. 

Through steric hindrance and conjugative effects, these ionic phosphonium salts are very stable to hydrolysis. This, coupled with the lipophilic nature of the cation, results in a very soft, loosely bound ion pair, making materials of this type suitable for use as catalysts in anionic polymerization [8 - 13]. Phosphazene bases have been found to be suitable catalysts for the anionic polymerization of cyclic siloxanes, with very fast polymerization rates observed. In many cases, both thermodynamic and kinetic equilibrium can be achieved in minutes, several orders of magnitude faster than that seen with traditional catalysts used in cyclosiloxane polymerization. Exploiting catalysts of this type on an industrial scale for siloxane polymerization processes has been prevented because of the cost and availability of the pho hazene bases. This p r describes a facile route to materials of this type and their applicability to siloxane synthesis [14]. 

With still longer intervening organic moieties, strain-free cyclosiloxanes result, e.g., the seven-membered 2,2,7,7-tetramethyl-l-oxa-2,7-disilacycloheptane and its polymers . The ultimate extension of this cyclocarbosiloxane synthesis is illustrated by the next example. Hydrosilylation of both ends of 1,7-octadiene with HMejSiCl gives an adduct that upon hydrolysis yields -f-Me2Si(CH2)8SiMe20-, which in turn affords the 22-membered dimeric and 11-membered monomeric cyclosiloxanes upon alkaline thermolysis . 

Selective and Stepwise Synthesis of Cyclosiloxanes with Mixed and "Inorganic" Substituents... 

Keywords Cyclosiloxanes / Disilanyloxy Compounds / Synthesis / Structure... 

Investigations on synthesis, structure and reactivity of siloxanes [I, 2] have been continued by attempts to synthesize cyclosiloxanes with at least one Si-Si-O group instead of Si-O. Only a few such compounds are known until now [3-6]. Such siloxanes could be interesting due to the... 

Monomer Syntheses. The polymer synthesis proceeds mainly from the dichloro- and trichlorosilanes, which can be produced by three different synthetic routes. In contrast, the polymerization of cyclosiloxane plays a limited commercial role. 

The reactivity of cyclosiloxane with the 3,3,4,4,5,5, 6,6,6-nonafluorohexyl group and its application to fluorosilicone synthesis was carefully studied by Furukawa et al. [27]. In contrast to polymerization of commercially available l,3,5-tra(3,3,3-trifluoropropyl)-1,3,5-trimethylcyclotrisiloxane (CF3-D3), polymerization of l,3,5-tra(3,3,4,4,5,5,6,6,6-nonafluorohexyl)- 1,3,5 -trimethylcyclotrisiloxane (C4F9-D3) with sodium hydroxide yielded 1,3,5,7-tetrakis(3,3,4,4,5,5,6,6,6-nonafluorohexyl)-l,3,5,7-tetramethylcyclotetrasiloxane [C4F9CH2CH2(CH3) SiO]4 (C4F9-D4) as the major product. On the other hand, it was reported that polymerization of C4F9-D3 with trifluoromethanesulfonic acid proceeded in... 

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