Bis-silanol

Mark and his co-workers reported the reinforcement of poly(dimethylsiloxane) networks by silica gel particles [1-6]. For example, bis(silanol)-terminated poly-(dimethylsiloxane) was reacted with tetraethoxysilane in the presence of acid-catalyst to produce the reinforced siloxane networks. The reaction proceeded homogeneously. The content of the silica filler can be controlled by the feed ratio of polysiloxane and tetraethoxysilane. 

Heteropolycondensation of Bis-silanols, III, with Diacetoxysilanes. Heteropolycondensation of bis-silanols, III, was investigated since this approach appeared to offer a relatively rapid preparative route to a number of various siloxane-modified poly(arylene carbonates) which were required in order to obtain structure-properties correlations for such polymers. 

In addition, polymers containing an odd number of silicon atoms in the siloxanylene segment can be prepared by this approach. However, reaction conditions employed in condensation of bis-silanols, III, with diaminosilanes (41) or siloxazanes (42) led to the cleavage of the carbonate group. Consequently, the recently reported silanol-acetoxysilane polycondensation reaction (43) was investigated for the polycondensation of bis-silanols, III, with diacetoxysilanes or diacetoxydisiloxanes (reaction 3). 

It was found that the reaction conditions which were optimized for the synthesis of poly(arylene siloxanylenes) (43) could be employed for the synthesis of siloxane-modified poly-(arylene carbonates). 2,4,6-Trimethylpyridine (collidine) was selected as the most suitable of all catalysts investigated (43) for the synthesis of the siloxane modified poly(arylene carbonates). Properties of polymers prepared by this method are given in Table I. In comparision to the phosgene-catalyzed homo-polycondensation of bis-silanols, III, the inherent viscosities... 

Polycondensation of Bis-silanols, III, with Diacetoxy-silanes, Diacetoxydisiloxanes or Diacetoxytrisiloxanes. A mixture of 12.00 mmole of a bis-silanol, III, 12.00 mmole of a diacetoxysilane, diacetoxydisiloxane or diacetoxytrisiloxane,... 

On heating, these bis-silanols undergo quantitative dehydration to the siloxanes... 

Fig. 7 Bis-silanol PDMS condensation chromatogram carried out during three days. Reaction conditions L OH, O.Smmol, 2.1g 0.004mmol, 2mg L H, O.Smmol, 0.067g in 5mL toluene.

Treatment of 7 with DMD leads to the short-lived bis-silanol A. However, this intermediate undergoes intramolecular condensation, resulting immediately in the formation of the tungsten complex 8 bearing a disiloxane unit bridging the cyclopentadienyl ligand and the metal center. 8 is... 

An alternative synthesis of the tungsten bis-silanol A starts with the regioselective chlorination of the metal-bound Si-H function of 6 with PdCli. The corresponding tungsten chlorosilane 9 is isolated in 85% yield as a yellow solid (Scheme 2). 

The treatment of 9 with DMD in acetone at -78 °C leads to the tungsten chlorosilane with a cyclopentadienyl-flxed silanol unit (B), which as the bis-silanol A shows fast intramolecular condensation to 8. 

We have synthesized some novel silarylene and silarylenesiloxane polymers via dicarbanions prepared from Lochmann s base. Lochmann s base, a powerful metalating reagent composed of equimolar amounts of n-butyl lithium and potassium r-butoxide in a hydrocarbon, has been used to dimetalate compounds such as m-xylene, 4,4 -dimethylbi-phenyl, and 2,3-dimethyl-1,3-butadiene in good yields. In this work the dicarbanion of m-xylene and 4,4 -dimethylbiphenyl have been used to prepare silicon containing monomers and polymers by two different routes. The first route involves a 1 1 condensation reaction between the dicarbanion and a dichlorodiorganosilane to produce a condensation polymer. The second route involves reaction of the dicarbanion with a chlorodiorganosilane which is then converted to a bis(silanol) and then polymerized. Spectroscopic as well as thermal characterization will be presented on the polymers which have been described. 

The impetus for their research was to discover a new class of viscoelastic polymers which exhibited good thermal stability and broad use temperatures for use as fuel-resistant sealants. The synthetic methods used to prepare polymers like 9 are similar to those methods which were used in studies mentioned previously. For 2 (x = 0), the bis(silanol) was prepared and then condensed using tetramethylguanidine 2-ethylhexoate as a catalyst to prepare the polymer. For 9 (x = 1) the appropriate bis(silanol) was condensed with a bis(dimethylamino)silane, and for 9 (x = 2) the appropriate bis(silanol) was condensed with a bis(dimethylamino)disiloxane. Table 3 relates some of the various properties found from polymers prepared using these methods. 

Polymer Preparation. In order to prepare silicon containing polymers which include the m-xylyl and dimethylenebiphenyl moieties, two distinct polymerization routes were chosen. The first route consists of condensation of a dichlorodialkyl(or aryl)silane with a dicarbanion, namely 12 or 12. The material which is formed consists of an all silicon-carbon and carbon-carbon backbone. The second polymerization utilizes the bis(silanol) monomers discussed in the previous section. These materials are heated and undergo a self condensation reaction to form polymers which contain silicon-carbon, silicon-oxygen, and carbon-carbon bonds in the backbone. 

From bis-silanol monomers, themselves prepared either via an organo-metallic route or via hydrosilylation of a,c -dienes. The bis-silanol monomers are then polymerized to give hybrid homopolymers or condensed with difunctional silanes to give copolymers (cf Scheme 2). 

Synthesis of Hybrid Silicones Starting from Bis-Silanol Monomers... 

---