Stabilization mechanism of 2D energetic polymer intercalated HMX (1,3,5,7-Tetranitro-1,3,5,7-tetrazocane) crystals

The intercalation of the two-dimensional triamino guanidine-glyoxal polymer (TAGP) into 1,3,5,7-Tetranitro-1,3,5,7-tetrazocane (HMX) crystals, forming so-called hybrid qy-HMX crystals, has been found to be able to significantly increase the energy density and thermal stability of HMX. However, the physicochemical interactions between them remain to be explored. This study conducted theoretical calculations and in situ X-ray diffraction (XRD) experiments to investigated these interactions, particularly for the conformational transition of the hybrid crystal. The results showed that the presence of TAGP would constrain the conformation and arrangement of HMX molecules. Bond length analysis indicated that the TAGP intercalation can shorten N–N bond lengths of HMX, which effectively suppresses the thermal decomposition initiated by the rupture of N–NO₂. The In situ XRD simulations and experiments confirmed the improvement in thermal stability of qy-HMX in comparison to the raw β-HMX, raising by stronger resistance to polycrystalline transitions of qy-HMX. The enhanced stability was attributed to the constraining effect of TAGP, forcing HMX molecules to maintain a ‘boat-chair’ conformation. Once constraint with TAGP formed, the ‘boat-chair’ conformation can exist stably even at room temperature, resulting in remarkable thermal stability of qy-HMX. Besides, electronic density of states calculations suggested that the intercalation of TAGP may decrease the number of electronic states in qy-HMX crystals near the Fermi level, contributing to the thermal stability improvement. In addition, further analysis on the interaction mode between HMX and TAGP molecules confirmed the presence of hydron bond and van der Waals interactions, which should be responsible for the stabilization of hybrid qy-HMX crystals. This study provided insights in the stabilization mechanism of TAGP Intercalated HMX, and it indicated this strategy can offer an efficient method for developing high-performance and low-sensitivity energetic crystals.