High-molecular polysilane and method for the production thereof for producing pre-ceramic molded bodies

Abstract

A method produces a polysilane by reacting at least two silane monomers and at least one alkali metal. The silane monomers have the following structural units: at least one aryl group, at least one alkyl group, at least one alkenyl group, and at least three halogen atoms. Wherein at least three of the halogen atoms are bonded to a silicon atom of one of the silane monomers, and the reaction step takes place in an ether-containing solvent, particularly preferably dioxane. The obtained polysilane has a high molecular mass and, at 100° C., a viscosity of 1,500 to 3,000 Pa·s. The polysilane is very suitable for being processed to form silicon carbide fibers and fiber composites.

1 . A method for producing a polysilane, which comprises the steps of:
 reacting (i) at least two silane monomers and (ii) at least one alkali metal in an ether-containing solvent, the silane monomers containing the following structural units:
 at least one aryl group; 
 at least one alkyl group; 
 at least one alkenyl group; and 
 at least three halogen atoms, at least three of the halogen atoms being bonded to a silicon atom of one of the silane monomers. 
   
     
     
         2 . The method according to  claim 1 , wherein ether of the ether-containing solvent contains at least two oxygen atoms. 
     
     
         3 . The method according to  claim 1 , wherein the ether-containing solvent contains 50 to 100% dioxane. 
     
     
         4 . The method according to  claim 1 , which further comprises using the alkali metal in an excess of at least 10% with respect to an amount of halogen in educts. 
     
     
         5 . The method according to  claim 1 , which further comprises adding the alkali metal step by step in parallel with an addition of the silane monomers to a reaction mixture. 
     
     
         6 . The method according to  claim 1 , which further comprises using a reaction initiator during the reacting step, and the initiator contains the following structural units:
 a silicon atom;   at least one halogen atom bonded to the silicon atom; and   at least two sterically hindering groups bonded to the silicon atom.   
     
     
         7 . The method according to  claim 1 , which further comprises adding 0.01 to 0.25 mol. % of an initiator to the alkali metal dispersion prior to an addition of remaining silane monomers. 
     
     
         8 . The method according to  claim 1 , wherein the ether-containing solvent contains 100% dioxane. 
     
     
         9 . The method according to  claim 1 , which further comprises using the alkali metal in a range of 10 to 20% with respect to an amount of halogen in educts. 
     
     
         10 . The method according to  claim 1 , which further comprises adding the alkali metal in at least 4 steps in parallel with an addition of the silane monomers to a reaction mixture. 
     
     
         11 . The method according to  claim 1 , which further comprises adding 0.06 to 0.1 mol. % of an initiator to the alkali metal dispersion prior to an addition of remaining silane monomers. 
     
     
         12 . A polysilane produced by a process which comprises the steps of:
 reacting (i) at least two silane monomers and (ii) at least one alkali metal in an ether-containing solvent, the silane monomers containing the following structural units:
 at least one aryl group; 
 at least one alkyl group; 
 at least one alkenyl group; and 
 at least three halogen atoms, at least three of the halogen atoms being bonded to a silicon atom of one of the silane monomers. 
   
     
     
         13 . The process according to  claim 12 , wherein the polysaline having the at least one aryl group, the at least one alkyl group and the at least one alkenyl group, has a molecular weight of at least 5,000 Da. 
     
     
         14 . The process according to  claim 12 , wherein the polysilane, calculating on a basis that a total of the following groups in the polysilane is 100%, comprises 40 to 95% alkyl groups, 5 to 30% alkenyl groups, 10 to 30% aryl groups, and 0.1 to 10 hydrogen atoms. 
     
     
         15 . The process according to  claim 12 , wherein the polysilane has a viscosity of 1,500 to 3,000 Pa s at 100° C. 
     
     
         16 . The process according to  claim 12 , which further comprises processing the polysilane by melt spinning or dry spinning to form fibers having a diameter of 1 to 100 μm. 
     
     
         17 . A process for producing silicon carbide fibers, which comprises the steps of:
 producing polysilane fibers by reacting (i) at least two silane monomers and (ii) at least one alkali metal in an ether-containing solvent, the silane monomers containing the following structural units:
 at least one aryl group; 
 at least one alkyl group; 
 at least one alkenyl group; and 
 at least three halogen atoms, at least three of the halogen atoms being bonded to a silicon atom of one of the silane monomers; 
   pyrolysing the polysilane fibers; and   processing the polysilane fibers to form ceramic fibers.   
     
     
         18 . The process according to  claim 17 , which further comprises chemically or physically curing the polysilane fibers prior to performing the pyrolysing step. 
     
     
         19 . A method of producing silicon-carbide-containing molded bodies, which comprises the steps of:
 producing silicon carbide fibers by producing polysilane fibers by reacting (i) at least two silane monomers and (ii) at least one alkali metal in an ether-containing solvent, the silane monomers containing the following structural units:
 at least one aryl group; 
 at least one alkyl group; 
 at least one alkenyl group; and 
 at least three halogen atoms, at least three of the halogen atoms being bonded to a silicon atom of one of the silane monomers; 
   pyrolysing the polysilane fibers;   processing the polysilane fibers to form ceramic fibers; and   forming the ceramic fibers into a silicon-carbide-containing molded body.   
     
     
         20 . The method according to  claim 19 , which further comprises using the silicon-carbide containing molded body in one of lightweight construction, electrical industry, space travel, motor vehicle construction and aircraft construction.