We monitor the T-jump pyrolysis and combustion reactions of diisopropyl methylphosphonate (DIMP) via FTIR and kinetic FTIR. DIMP is heated at 10 degrees C/s, similar to 1800 degrees C/s, and similar to 18,000 degrees C/s to temperatures between 500 degrees C and 1200 degrees C in nitrogen, air, and an oxygen-rich environment. We observe propene, isopropyl methylphosphonate (IMP), and methylphosphonic acid (MPA) as final decomposition products. In addition, we identify 2-propanol in the early phase of the reaction. The results indicate that DIMP has two possible decomposition pathways: (1) A two-step decomposition process in which DIMP first transfers an H atom from the OCH(CH3)(2) group to the double-bonded oxygen through a six-membered ring transition state and forms IMP and propene. Subsequently, IMP decomposes into either propene and MPA or 2-propanol and methyl(oxo)-phosphoniumolate (MOPO). (2) DIMP transfers an H atom from the OCH(CH3)(2) group to the 0 atom of the other OCH(CH3)(2) group through a different six-membered ring and simultaneously forms MOPO, propene, and 2-propanol. Our theoretical calculation indicates that the energy barriers for the two reaction pathways are 36.5 kcal/mol (pathway 1, 1st step), 49.9 kcal/mol (pathway 1, 2nd step), and 51.2 kcal/mol (pathway 2), respectively. When using a heating rate of 10 degrees C/s, pathway (1) is the major reaction in the system; using a heating rate of similar to 18,000 degrees C/s, pathway (2) is the most probable reaction; and when the heating rate is similar to 1800 degrees C/s, both pathways are observed during the early phase of the reaction. When heated in air and an oxygen-rich environment, we observe the same decomposition products plus CO and CO2. (C) 2018 Published by Elsevier Inc. on behalf of The Combustion Institute.