Preparation method of polysilazane for preparation of SiCN nonoxide ceramic fibre

A preparation method of polysilazane for preparation of SiCN nonoxide ceramic fibre relates to a preparation method of high molecular weight polysilazane. According to the method, a protective measure is taken by introducing nitrogen into a reaction system; a repetitive ammonolysis reaction is carried out on reaction products from the first step to ensure that the reaction in the first step is completely finished so as to raise reaction yield; and based on the products from the first step, activated thermopolymerization is carried out for intermolecular crosslinking so as to obtain high molecular weight polysilazane. By a systematic desensitization method, hydrolysis of raw materials, methyl hydrogen-dichlorosilane and methyl vinyldichloridesilane, which are sensitive to water and the air, is prevented so as to guarantee that the reactions can be carried out smoothly, and the purpose of raising quality and yield of the low polymer product is achieved. By a repetitive reaction method, the ammonolysis reaction is more thoroughly completed so as to achieve the purpose of uniform molecular weight of the low polymer. By the activated thermopolymerization method, intermolecular crosslinking of the low polymer is realized to form a high polymer so as to achieve the purpose of obtaining the high molecular weight PSZ (200,000).