In this work new energetic prepolymers are synthesised and characterised. The structure of the prepolymers exhibits the 1,3,5-s-triazine ring with lateral chains derived from the epichlorohydrin ring opening. The chlorine atoms in these precursors are here substituted by azido groups. The presence of these groups was confirmed by FTIR and 1H NMR spectroscopy and elemental and thermal analysis. OH group content in the energetic prepolymers was found slightly lower than expected having in view the used inert precursors, while molar mass values were similar. Whereas the precursors show an endothermic thermal decomposition, the synthesised prepolymers show a clear exothermic thermal decomposition in DSC analyses. Due to the presence of the 1,3,5-s-triazine ring, the exothermic peaks were observed in a wide range of temperatures. The measured glass transition temperatures vary from −15.5 °C to −43.3 °C. High densities and a wide range of viscosities were found.