Synthesis of Fused-Nitrogen-Based Energetic Ionic Liquids: Low-Temperature and High Energy Plasticizers for Solid Propellants.

Herein, we liquefied fused-nitrogen compounds as a viable alternative to traditional high-sensitivity plasticizers by employing ionic liquid engineering. We synthesized three novel fused-nitrogen compounds N⁶-(1,3,4-oxadiazol-2-yl)-[1,2,4]triazolo[4,3-b][1,2,4,5]tetrazin (DTOZ), N⁶-(5-diamine-1,2,4-oxadiazole-3-yl)-[1,2,4]triazolo[4,3-b][1,2,4,5]tetrazin (DTFA) and N⁶-(4,5-dicyanoimidazol-2-yl)-[1,2,4]triazolo[4,3-b][1,2,4,5]tetrazin (DTIZCN) based on triazolo-tetrazine backbone having high energy and low sensitivity (impact sensitivity > 40 J) by incorporating amino nitrogen heterocycles. The decomposition temperature (Td) and enthalpy of formation (ΔHf) of DTIZCN were 327.9°C and 1118.7 kJ mol⁻¹, respectively, while the density of DTOZ (1.814 g cm⁻³) was comparable to cyclotrimethylenetrinitramine (RDX). Nine fused-nitrogen-based energetic ionic liquids (EILs), with ΔHf between 204.9 and 531.1 kJ mol⁻¹, were synthesized via neutralization of three aliphatic quaternary ammonium cations. The DDA-DTOZ showed a low glass transition temperature (Tg = -46.1°C). Fused-nitrogen compounds demonstrated improved performance compared to conventional energetic materials, with a maximum specific impulse performance of 267.69 s being reached for DODA-DTFA with 14% plasticizer. Fused-nitrogen-based EILs showed application potential in high-energy propellants.