THERMAL-DECOMPOSITION OF ENERGETIC MATERIALS .54. KINETICS AND NEAR-SURFACE PRODUCTS OF AZIDE POLYMERS AMMO, BAMO, AND GAP IN SIMULATED COMBUSTION

Kinetics of weight-loss during programmed heating at 150-degrees-C/s were determined by simultaneous mass and temperature change (SMATCH)/FTIR spectroscopy of the polymers 3-azidomethyl-3-methyloxetane (AMMO), 3,3'-bis(azidomethyl)oxetane(BAMO), and glycidyl azide polymer (GAP). The kinetics match the burn rate of GAP extrapolated to the same pressure and temperature range, which suggests that SMATCH/FTIR gives an instantaneous microscale simulation of macroscale combustion at those pressure and temperature conditions. SMATCH/FTIR spectroscopy enables the gases that leave the surface and form the earliest stage of the flame zone to be identified. Small molecules are formed by BAMO and GAP, but some large fragments are evolved by AMMO. Kinetic constants were determined for AMMO, BAMO, and GAP by isothermal and nonisothermal thermogravimetric analysis (TGA). Comparing these data to SMATCH/FTIR kinetics reveals that the accelerating rate of change of mass with time (d-alpha/dt) at small alpha controls the temperature dependence of the TGA rate constant, while the total mass present at a particular time (1 - alpha) controls the SMATCH/FTIR kinetics. Irrespective of chemistry differences at low and high heating rates, TGA kinetics would be expected to fail to predict the combustion behavior because the specific reaction rates in the lower and higher temperature ranges fail to connect by factor of several thousand.