LOW VISCOSITY, CROSSLINKABLE LIQUID POLYSILANES

摘要

Low viscosity, crosslinkable polysilanes that are liquid at ambient temperatures and essentially free of volatiles, well adapted for conversion into silicon carbide ceramics at elevated temperatures, are prepared by (a) reacting at least one silane monomer of the formula (1): R1R2SiCl2 (1) in which R1 is a hydrogen atom or a hydrocarbon radical and R2 is a vinyl radical, with at least one organic or organosilicon monochlorinated comonomer, in the presence of molten sodium in an organic solvent and wherein the ratio r1 of the number of moles of the silane monomer of formula (1) to the number of moles of the monochlorinated comonomer ranges from 0.5 to 2 and the solvent includes toluene and dioxane, (b) cooling the reaction medium and separating it, characteristically by filtration, into (i) a liquid phase which includes such solvent and the major fraction of low molecular weight polysilane in liquid and/or dissolved state and (ii) a solid phase which includes sodium, sodium chloride and high molecular weight polysilane, and (c) recovering desired low viscosity polysilane from such liquid phase and preferably oxidizing the sodium present in the solid phase.