In this publication the glass transition, melting behavior, cure behavior, and thermal stability of LaRC PETI-5 have been extensively studied utilizing differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The material used here was subjected to different thermal history (cumulative cure and individual cure) including an isothermal cure. The extent of cure for the partially cured resin was evaluated taking into account the residual solvent in the resin with the aid of a correction factor. The data show that the thermal history for the imidization reaction may influence the extent of cure for the partially cured LaRC PETI-5. The reaction of the C equivalent to C bonds in the phenylethynyl groups located in the imide polymer chain ends is completed to produce a fully cured LaRC PETI-5 within 1 h at 350 degrees C in air. The result is very consistent with the result obtained using Fourier Transform infrared (FT-IR) spectroscopy in the previous work. This study also demonstrates that no reaction takes place above 350 degrees C prior to degradation. LaRC PETI-5 with a molecular weight of 2500 g/mol has excellent thermal stability up to 550 degrees C as long as it is fully imidized. The result of the isothermal stability suggests that this material may be used without significant loss of its integrity for extended periods of time below 450 degrees C. (C) 2000 John Wiley & Sons, Inc.