https://doi.org/10.1351/goldbook.15299
Polymer composed of macromolecules containing exclusively alternating nitrogen and silicon atoms in the backbone: \[\ce{-[-NR^{1}\bond{-}SiR^{2}\!\,R^{3}\bond{-}]_{n}\bond{-}}\] where \(\ce{R^1}\), \(\ce{R^2}\), and \(\ce{R^3}\) are each hydrogen or an alkyl or aryl group.
Note: Polysilazanes can comprise both silicon and nitrogen branching points, the former being formed from ammonia and the latter from, for example, alkyltrichlorosilanes or tetrachlorosilane used as monomers: 
where \(\ce{R^1}\), \(\ce{R^2}\), and \(\ce{R^3}\) are each hydrogen or an alkyl or aryl group.
Example: 