Simultaneous monitoring of the imidization and cure reactions of LaRC PETI-5 sized on a braided glass fabric substrate by dynamic mechanical analysis

The imidization and cure reactions of a thin film of phenylethynyl imide oligomer (LaRC PETI-5, Mn=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 δ 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°C. The Tg of the fully cured LaRC PETI-5 was measured as 287°C. The maximum in the tan δ curve transformed with increasing cure temperature from a triplet due to completion of imidization above 250°C to a singlet after completion of the cure reaction. The maximum of the singlet tan δ curve at 287°C is identified as the Tg 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°C. This result also confirms that after cumulative or isothermal processing, LaRC PETI-5 can be fully cured at 350°C for 1 h. These results agree well with the Fourier Transform infrared spectroscopy and differential scanning calorimetry results reported earlier.