Method for synthesizing high-ceramic-yield polycarbosilane

The invention discloses a method for synthesizing high-ceramic-yield polycarbosilane. The method comprises the following steps: mixing polycarbosilane of which the molecular weight is 500-1,500 with an allyl compound according to the proportion 100:(12-4); dissolving the mixture into dimethylbenzene; putting into a reaction vessel; adding an organic lithium reagent; heating under the protection of protection gas for reacting; controlling the highest reaction temperature at 100-150 DEG C; preserving heat for reacting for 2-8 hours; after finishing the reaction, filtering insoluble substances; removing a solvent by evaporating to obtain the high-ceramic-yield polycarbosilane. The method has the characteristics of easiness in controlling of the reaction conditions, simple and convenient steps, self-crosslinking performance of a product, and adjustable Si-H and allyl content. The method can be used for preparing liquid-state or solid-state high-ceramic-yield polycarbosilane conveniently.