Electrosynthesis Of Polysilanes

In the preparation of SiC fibers by preceramic polymer pyrolysis,the polycarbosilane should be split into liquid polysilanes and then rearranged under high temperature.This way to polycarbosilanes cannot gain various substituent groups and well proportioned molecular weight with drastic reacting conditions.And the procedure of PDMS-to-PCS is too complex to accomplish with several intermediate steps.Electrosynthesis is emerging in recernt years.Polysilanes can be reducted on the cathode in the electrolytic tank.Electrochemical mild condition contributes to the synthesis of polysilanes with orderly stryuture,narrow molecular weight distribution and high yield.Especially the active groups such as hydroxy and amino can be introduced into Si-Si chain.Electrosynthesis has good prospects,therefore,it is expected to replace Wurtz method to synthesize polysilanes.With the electrosynthesis of liquid polysilanes of small molecular weight,the synthesis process of polycarbosilanes can be greatly shortened,which reduces the cost of PCS.First,the effects of electrolyte and electrode on conductivity and product were explored with dichlorodimethylsilanes as monomers.it was found that Mg was proper in electrosynthesis and LiAlH₄ had the best conductivity in THF.However,because of the great symmetry of dichlorodimethylsilanes,the electrosynthesis cannot be easily carried out and the PDMS had a low yield.Therefore,the dichloromethylvinylsilanes were selected as monomers containing Si in the experiments.The polymethylvinylsilanes had the highest yield of 65.75%,the highest moleculer of 486and the highest ceramic yield of 58%when the electricity of 100 mA and the concentrition of 1.0 mol/L.The copolymerization of dichlorodimethylsilanes and dichloromethylsilanes was researched in order to prepare the polysilanes containing block structure.The effects of different proportion of the two kinds of monomers and the electricity on the electrosynthesis were explored.The polysilanes containing block structure with well proportioned molecular weight were prepared with the proportion of 1:1 and the electricity of 100 mA.The yield of the polysilane was 64.8%,the molecular weight was659.6 and the ceramic yield was 86%.A series of studies concerning LiAlH₄ were carreid out.Researches showed that LiAlH₄ had great conductivity in THF and accelerated the electrosynthesis of silane monomers.In the synthesis of polymethylvinylsilanes,the H in LiAlH₄ replaced part of C=C double bonds and formed Si-H,which then reacted with the rest of C=C double bonds under the condition of radical initiator and improved the effect of crosslinking.The electrosynthesis of PCS was also explored.Results showed that a polymer with high molecular weight and a structure similar to PCS could be electrosynthesized from（CH₃）₂SiCl₂ and CH₂Cl₂.