Nitrate-Functionalized Azetidines for Synergistic Combustion in Ammonium Perchlorate-Based Propellant Formulations

The development of high-performance energetic fuel components with rapid ignition characteristics is crucial for next-generation ammonium perchlorate (AP)-based composite propellants. Herein, we report a series of pyrimidine- and pyrazine-substituted azetidine nitrate esters (3, 6, and 9) and systematically investigate their structural, thermal, energetic, and combustion properties. Notably, compound 3 crystallized in two polymorphic forms (3 and 3'), revealing how crystal packing influences intermolecular interactions, density, and energetic performance despite identical molecular composition. All compounds exhibit favorable thermal stability, with decomposition temperatures ranging from 161 to 179 °C, high densities of 1.68-1.75 g cm-3, and moderate impact sensitivities (<2.5 J). Among them, compound 9 shows the highest energetic performance, with a detonation velocity of 7740 m s-1. To evaluate their potential as energetic fuel components, binary AP/fuel formulations with varying oxidizer-to-fuel ratios were prepared and assessed using combustion and hot-needle ignition tests. All formulations displayed rapid flame propagation and ignition delay times below 10 ms, while the formulation containing 5 wt % of AP with compound 3 achieved an exceptional short ignition delay of 1 ms. These findings demonstrate that nitrate-functionalized azetidines not only possess attractive intrinsic energetic properties but also exhibit remarkable fuel-oxidizer synergy with AP, enabling rapid ignition and efficient combustion. This work establishes pyrimidine and pyrazine-substituted azetidine nitrate esters as promising energetic fuel components for next-generation AP-based composite propellant formulations.