Molecular revelation of the thermal decomposition mechanism of glycidyl azide polymer in nitrate esters matrix

Glycidyl azide polymer (GAP), a high-energy and recyclable binder, can potentially enhance the energy of nitrate ester-plasticized polyether (NEPE) propellants. The thermal decomposition of binders in propellants is a crucial factor affecting engine safety. However, the thermal decomposition process of GAP in propellants remains unclear to date, and the precise atomic-level mechanism behind it remains elusive. In this study, we employed density functional theory (DFT) calculations and reactive force field molecular dynamics (ReaxFF-MD) simulations, combined with TG-DSC-FTIR-MS coupled tests, to investigate comprehensively the thermal decomposition process of GAP in nitrate esters matrix (NE-GAP). The study revealed that the decomposition process of NE-GAP involves five initial pathways and four stages. The nitrate esters (NEs) matrix provides a rich oxygen environment for GAP, resulting in a more complete decomposition process with minimal formation of clusters. In contrast to the pure component GAP (Pure-GAP), NE-GAP hardly generates amine products and uniquely forms C₂O₂ key intermediates. The decomposition products NO₂ and NO of NEs preferentially attack the N1 on the azido groups and the H3 on the ether chains of GAP, constituting 43 % of the total initial reaction frequency. The presence of NEs reduces the activation energy (Ea) for azido group cleavage by 65 % and for ether bond cleavage by 66 %. These insights highlight potential pathways for preventing the thermal decomposition of GAP in NEPE propellants from an atomic and molecular perspective.