Preparation of HMX/PMMA Composite Microspheres with Excellent Properties by Photoinitiated Emulsion Polymerization

High-energy insensitive energetic materials are currently a research focus. Octogen (HMX) is one of the best-performing nitramine explosives, but its poor crystal morphology causes high mechanical sensitivity, limiting its application. This study proposed a method combining spheroidization, nanosizing, and coating desensitization. Nano-SiO₂ and TiO₂ were used to modify methyl methacrylate (MMA), and HMX/PMMA composite energetic microspheres were successfully prepared with the assistance of an ultraviolet (UV) lamp for catalytic polymerization. Molecular dynamics simulations determined the optimal particle ratios, and the effects of modifier content on morphology, crystal form, thermal stability, mechanical properties, and static mechanical properties were experimentally investigated. The prepared HMX/PMMA/modifier microspheres exhibited uniform size, dense structure, excellent performance, and ideal coating. Thermal decomposition kinetics showed that the activation energy of HMX/PMMA/SiO₂ (0.75 wt% SiO₂) increased by 79.86 kJ/mol and 27.55 kJ/mol compared with raw HMX and HMX/PMMA, respectively. Its impact sensitivity was 3.6 times that of raw HMX, and its friction sensitivity was twice that of raw HMX. Static mechanical analysis revealed that the compressive strength of HMX/PMMA/SiO₂ (0.75 wt% SiO₂) and HMX/PMMA/TiO₂ (0.5 wt% TiO₂) microspheres increased by 7.3 MPa and 6.1 MPa, respectively, over HMX/PMMA, indicating significant improvement. Overall, HMX/PMMA/SiO₂ and HMX/PMMA/TiO₂ microspheres prepared by photoinitiated emulsion polymerization exhibited excellent thermal stability and mechanical properties.