Siloxanediols

The preparation and structures of siloxanediol derivatives has been reviewed29,184 but some representative examples of reactions are given below. Two general methods have been used to make metal siloxides from silanols one involves the direct reaction of a silanol with the metal derivative, usually an amide, alkoxide, halide or alkyl (to give amine, alcohol, HX or alkane byproducts respectively), while the second involves the preparation of a simple alkali metal derivative which can then be used as a siloxide transfer reagent for further synthesis. Only the direct route will be considered here. Two of the most useful siloxide transfer species, (MOPh2Si)20 (M = Li or Na), are... 

FIGURE 1. Hydrogen bonded chain structures in simple siloxanediols. Curves represent Si—O—Si backbone, dashed lines show hydrogen bonding... 

Eq. 2. Co-condensation reaction of silacyclobutene 1 with a.co-dimethyl-oligo-siloxanediols 2-5. 

Table 1. Copolymerization reaction of silacyclobutene I with siloxanediols 2-5.

This observation is supported by the data in Table 2, which lists the DSC results of the siloxanediols 3 - 5 as well as of the silacyclobutene containing copolymers 6 - 16. It has been found that the shift of the glass transition temperature is related to an increase of the silacyclobutene ratio. In the same way, the heat capacity change at the glass transition increases with increasing Slcyclobutene ratio. 

On the Acid- and Base-Catalyzed Reactions of Silanediols and Siloxanediols in Water... 

Summary The acid- and base-catalyzed reaction of some partially water-soluble silanediols XMeSi(OH)2 and siloxane-1,1-diols have been investigated preferably in the two-phase system water/toluene. The diols react in water only whereas the less water-soluble products of the primary reactions are dissolved in the inert toluene phase. The silanediols give condensation only, the siloxanediols also show Si-O-Si-cleavage. The distribution rates of the model compounds and the rate constants of the primary reactions in water have been investigated,... 

Silane- and siloxanediols are important intermediates in silicone synthesis. During the technical chloro- or alkoxysilane hydrolysis the primary-formed silanols and siloxanols react preferably in the aqueous phase due to their considerable water solubility. To get more information on these reactions in water we investigated some silane- and siloxanediols using a method already described [1]. 

M. W. Backer, J. P. Hannington, P. R. Davies, N. Amer type of endgroup seems to influence the crystallization behavior as well. Table 1. Copolymerization reaction of silacyclobutene 1 with siloxanediols 2-5. 

As basic products containing the Si-0 unit we used the siloxanediols H0-Me2Si-(0-Me2Si) -OH ( = 1,2,3). 

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. 

Reactions of 1,2-dichlorotetramethyldisilane with the siloxanediols according to Eq. 1 give the expected seven- to eleven-membered rings 1, II and III, cf [5, 6]. Reactions of 1,1,2,2-tetrachlorodimethyldisilane with one equivalent of siloxanediol give the monocyclic siloxanes IV, V, VI, VII (Scheme 1), for disiloxanediol (n = 1) as well with endocyclic as with exocyclic Si-Si, and for tri- and tetrasiloxanediol ( = 2, 3) with exocyclic Si-Si only. 

Scheme 1. Products of the reactions of 1,1,2,2-tetrachlorodimethyldisilane with one equivalent of siloxanediol.

The reaction of 1,1,2,2-tetrachlorodimethyldisilane with two equivalents of siloxanediol gives in a similar way the bicyclic cyclosiloxanes VIII, IX, X, for disiloxanediol ( = 1) with endocyclic Si-Si only, and for tri- and tetrasiloxanediol (n = 2,3) exclusively with exocyclic Si-Si (Scheme 2). The cyclocondensation in the 1,1-position at Si-Si seems to be favored, especially for at least eight-membered rings. 

The reaction of hexachlorodisilane with three equivalents of siloxanediol gives for all siloxanediols the tricyclic siloxanes with endocyclic Si-Si in all three rings (XI, XII, XIII) as well as the tricyclic siloxanes with Si-Si endocyclic in only one ring and exocyclic in the others (XIV, XV, XVI), according to Scheme 3. 

Scheme 3. Products of the reaction of hexachlordisilane with three equivalents of siloxanediol.

Short siloxanediols are important precursors in a wide variety of industrial products. They can be considered also as the monomeric representatives of a series of polymeric compounds which exhibit unique and highly desirable features such as specific rheological behaviour or thermal and chemical resistance. However, despite the broad knowledge about their physical and material properties, only limited information is available on the photoluminescence behaviour of these classes of compounds [1-6], In order to obtain a basic understanding of the influence of methyl and phenyl substituents on the photoluminescence of siloxanes, several siloxanediols have been prepared and investigated. 

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