A study of the kinetics of the microwave cure of a phenylethynyl-terminated imide model compound and imide oligomer (PETI-5)

The kinetic mechanism of the microwave cure of a simple 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, Mn 5000 g/mol) was studied. Dielectric properties of the model compound and PETI-5 were measured in the microwave range from 0.4 GHz to 3 GHz. FTIR was used to follow the cure of the model compound (PEPA-3,4′-ODA), while thermal analysis (DSC) was used to follow the cure of the PETI-5 oligomer. The changes in room temperature IR absorbance of phenylethynyl triple bonds at 2214 cm−1 of PEPA-3,4′-ODA as a function of cure time were measured after cure temperatures of 300, 310, 320, and 330 °C. The changes in the glass-transition temperature, Tg, of PETI-5 as a function of cure time were measured after cure at 350, 360, 370, and 380 °C, respectively. The Tg 's were determined to calculated the relative extent of cure, x, of the PETI-5 oligomer according to the DiBenedetto equation. For the model compound, the reaction followed first order kinetics, yielding an activation energy of 27.6 kcal/mol as determined by infrared spectroscopy. For PETI-5, the reaction followed 1.5th order, yielding an activation energy of 17.1 kcal/mol for the whole cure reaction, as determined by Tg using the DiBenedetto method. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2526–2535, 2000