Ultrasound polysilanes

We have been recently studying new pathways leading to polysilanes with low polydispersity and controlled structures. Our research is focused on three areas. The first one is low temperature reductive coupling in the presence of ultrasound. This leads to monomodal polymers with molecular weights in the range from Mn=50,000 to Mn=300,000 and polydispersities as low as Mw/Mn=1.20 (in addition to usually formed cyclic oligomers). 

More recently Kashimura et al. [96] has investigated the effect of ultrasound on the electroreductive synthesis of polysilanes, polymer germanes and related polymers using magnesium electrodes. They found that the presence of ultrasound greatly facilitated the reactions. 

The main method used to synthesise polysilanes 10.7 involves the thermally induced Wurtz coupling reaction of organodichlorosilanes with alkali metals [eqn (10.7)]. Although improvements in this process have been reported e.g. by the use of ultrasound), the harsh conditions for this reaction tend to limit the side groups that can be successfully introduced to non-functionalised alkyl and aryl units and makes scale-up unattractive. 

Ultrasound has been used for efficient and clean synthesis of polysilanes as well as further conversion of polysilanes to SiC by combining a reducing... 

Soluble crosslinked polysilane polymers have been made by reduction of n-hexyltrichlor-osilane with liq Na-K alloy promoted by ultrasound [cf Eq. (f)] °. 

This procedure, if necessary assisted by ultrasound, has now been proved to work effectively for the production of other polysilanes in substantial yield, in particular polyalkylsilanes. ... 

The yield of high molecular polysilanes is usually low (10-25%). Many attempts have been made to increase the yield of the high molecular mass polysilane by variation of the reaction conditions including inverse addition of a sodium suspension to the dichlorosilane, reactions in other solvents such as THF and at lower temperatures [33], addition of crown ethers [34] to increase the solubility of the alkaline metal, and the use of ultrasound [35] to accelerate the reaction. 

Polysilylenes (polysilanes) (34b) have received widespread interest. Their electronic properties are associated with a-electron conjugation in the silicon backbone which allows a significant delocalization of electrons along the chain. In the usual synthesis of polysilylenes, diorganodichlorsilanes (34a) are treated with sodium metal in a hydrocarbon diluent [173]. In order to recreate the surface of the sodium metal permanently ultrasound is used in these reactions [174,175]. 

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