The kinetic mechanism of the thermal cure of a phenylethynyl-terminated imide model compound, 3,4＇-bis[(4-phenylethynyl)phthalimido] diphenyl ether (PEPA-3,4＇-ODA) and a phenylethynyl-terminated imide oligomer PETI-5 (MW 5000 g/mol) was studied. FTIR was used to follow the cure of the model compound, while thermal analyses (DSC) was used to follow the cure of the PETI-5 oligomer. The changes in IR absorbance of phenylethynyl triple bonds at 2214 cm(-1) of PEPA-3,4＇-ODA as a function of cure time were detected at 318, 336, 355, and 373 degrees C, respectively. The changes in the glass transition temperature, T-g, of PETI-5 as a function of time were measured at 350, 360, 370, 380, and 390 degrees C, respectively. The DiBenedetto equation was applied to define the relative extent of cure, x, of the PETI-5 oligomer by T-g. For the model compound, the reaction followed first order kinetics, yielding an activation energy of 40.7 kcal/mol as determined by infrared spectroscopy. For PETI-5, the reaction followed 1.5th order, yielding an activation energy of 33.8 kcal/mol for the whole cure reaction, as determined by T,using the DiBenedetto method. However, the cure process of PETI-5 just below 90% by this method followed first-order kinetics yielding an activation energy of 37.2 kcal/mol.