Thermal behaviors and Decomposition Mechanism of PNIMMO with CL-20

To investigate the thermal decomposition mechanism between Poly(3-nitratomethyl-3- methyloxetane) (PNIMMO) and 2, 4, 6, 8, 10, 12-Hexanitrohexaazaisowurtzitane (CL-20), the thermal decomposition of PNIMMO, CL-20 and PNIMMO+CL-20 mixture under different conditions was studied using differential scanning calorimetry (DSC), thermogravimetric-differential scanning calorimetry-mass spectra-fourier transform infrared spectrometer (TG-DSC-MS/FTIR) and in-situ FTIR experiments. As a result, the exothermic peak temperature of the PNIMMO+CL-20 mixture shifts to lower values under both closed and open circumstances compared to CL-20. Different kinetic parameters and models were obtained for the three decomposition steps in the mixture. The first step follows the random chain scission model (L2) at α<0.5, and the phase boundary controlled reaction model (R3) at α>0.5. The second/third step is between the random chain scission model (L2) and the first-order reaction model (F1) at α<0.5, and conforms to the first-order reaction model (F1) at α>0.5. Thus, the decomposition of PNIMMO controls the initial speed, while the removal of the nitro group in CL-20 controls the later step. Combined with the analysis of gas products and condensed phase, PNIMMO speeds up the N—NO₂ bond breaking in CL-20 but doesn't alter its initial breakdown route.