The imidization and cure reactions of a thin film of phenylethynyl imide oligomer (LaRC PETI-5, M-n = 2500 g/mol) applied to a glass fabric and processed under cumulative and isothermal heat-treatment conditions have been measured. Three distinguishable peaks were detected in the tan delta curves, which give useful information on the glass transition temperature, imidization temperature, and cure reaction temperature. The degree of imidization or cure reaction occurring during the cumulative and isothermal cure processes is related to the presence and size of the imidization peak and the cure reaction peak. The rate of cure increases substantially above 250 degreesC. The T-g of the fully cured LaRC PETI-5 was measured as 287 degreesC. The maximum in the tan delta curve transformed with increasing cure temperature from a tripler due to completion of imidization above 250 degreesC to a singlet after completion of the cure reaction. The maximum of the singlet tan delta curve at 287 degreesC is identified as the T-g of the LaRC PETI-5 polyimide. It is concluded that the dynamic mechanical behavior of LaRC PETI-5 strongly depends on thermal history, especially above 300 degreesC. This result also confirms that after cumulative or isothermal processing, LaRC PETI-5 can be fully cured at 350 degreesC for 1 h. These results agree well with the Fourier Transform infrared spectroscopy and differential scanning calorimetry results reported earlier. (C) 2001 Published by Elsevier Science Ltd.