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-termi nated imide model compound, 3,4'-bis[(4-phenylethynyl)phthalimido]diphenyle ther (PEPA-3,4'-ODA) and a phenylethynyl-terminated imide oligomer (PETI-5, M-n 5000 g/mol) was studied. Dielectric properties of the model compound a nd 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 th ermal analysis (DSC) was used to follow the cure of the PETT-5 oligomer. Th e changes in room temperature IR absorbance of phenylethynyl triple bonds a t 2214 cm(-1) of PEPA-3,4'-ODA as a function of cure time were measured aft er cure temperatures of 300, 310, 320, ana 330 degrees C. The changes in th e glass-transition temperature, T-g, of PETI-5 as a function of cure time w ere measured after cure at 350, 360, 370, and 380 degrees C, respectively. The T-g's were determined to calculated the relative extent of cure, x, of the PETI-5 oligomer according to the DiBenedetto equation. For the model co mpound, 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 k cal/mol for the whole cure reaction, as determined by T-g using the DiBened etto method. (C) 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2526-2535, 2000.