Preparation, thermal cure and ceramization of liquid silazane oligomeric resins

Liquid silazane oligomers (LSZ) were prepared via co-ammonolysis of methyldichlolrosilane, methyltrichlorosilane and trimethylchlorosilane, and liquid polysilazanes were subsequently synthesized via the prepolymerized chain extention of LSZ with hexamethylenediisocyanate (HDI) in nucleophilic addition reaction. In the prepolymerization of LSZ and HDI, the viscosity of PSZ gradually increases with the increase of HDI amount, becoming a gel-like solid product. The PSZ is stable as a liquid or the PSZ will become a solid after it is as a liquid for 48 h when HDI amount is <10%. The thermal cure exhibits two-stage exotherm when the HDI increases in PSZ, i.e., one exothermic peak at 60-135℃ shifted to lower temperature and another exothermic peak at 170-250℃. Also, the chain extention prepolymerization eliminates the volatiles in the thermal cure. The ceramic yield of PSZ increases with the increase of HDI dosage in PSZ formulation (i.e., the ceramic yield is 22.6 for LSZ, 43.2% for LSZ-5% HDI, and 58.7% for LSZ-HDI).