Synthesis of Liquid Polysilazoxanes for Si?O?C?N Ceramics With Adjustable Composition and High-Temperature Properties

Preparing polysilazoxanes with a controlled molecular structure is the ideal route for fabricating Si  O  C  N ceramics with adjustable composition and properties. In this paper, liquid polysilazoxanes were synthesized via a controlled substitution reaction between trichlorosilane and alcohols (R  OH), followed by the condensation with ammonia. By adjusting the alkyl groups (R tert -butyl, dioxane and triazolylmethyl) of alcohols, three kinds of polysilazoxanes with Si  N  Si backbones, but different side chains were synthesized. During high-temperature pyrolysis, tert -butoxy groups in polysilazoxanes are easily removed, producing low-carbon (< 4 wt%) ceramics, while dioxane and triazolylmethyl groups decompose to form oxygen-rich and nitrogen-rich ceramics, respectively. Due to the composition distinction, the resulting Si  O  C  N ceramics showed quite different high-temperature behavior. This report provides a direct and effective method for obtaining polysilazoxanes with a controlled molecular structure, which is useful for fabricating Si  O  C  N ceramics with improved high-temperature performance.