IR spectroscopic study on the second thermal decomposition of the thermal decomposition residues of hexanitrohexaazaisowurtzitane (HNIW)

Residue 1 (Res. 1) and Residue 2 (Res. 2) with mass loss of 91.8% and 90.1% were prepared. The Res. 1 were heated to 300, 400, 550, 600, 800°C by thermogravimetry-differential scanning calorimetry (TG-DSC) in an argon atmosphere at a heating rate of 10°C/min. Samples of Res. 1-300, Res. 1-400, Res. 1-550, Res. 1-600, Res. 1-800 were obtained. The results show that the argon atmosphere is favourable to production of cyano-group (-CN) and the air atmosphere is favourable to production of carbodiimide. In-situ IR spectroscopy was applied to investigate the residues of HNIW above 232.0°C at a heating rate of 10°C/min in the air atmosphere to reveal forming mechanism of canbodiimide. It is discovered that the active intermediate-isocyanate come from cleveage and oxidation of C-C bonds and a part of C-N bonds. Then reactions between isocyanate and coherent functional groups proceed to produce carbodiimide. The space stucture of the residue at 454.7°C is discussed. Two planes of the polymer fragments which connected to two sides of carbodiimide are probably coplanar or perpendicular with each other.