Determining the gel point of an epoxy-hexaanhydro-4-methylphthalic anhydride (MHHPA) system

The DEBGA–MHHPA epoxy system has found increasing applications in microelectronics packaging for which the ability to understand and model the cure kinetics mechanism accurately is crucial. The present article reports on the work done to elucidate accurate knowledge of the gel point by rheological methods. To determine the gel point using the G′–G″ crossover method was found not to be accurate, and the gel point obtained by this method was found to be frequency-dependent. Using the point where tgδ was found independent of the frequency can accurately define the gel point at different temperatures. At the gel point determined by this method, G′ and G″ were found to follow the same power law, demonstrating the accuracy of the method in determining the gel point. The scaling exponent obtained was 0.75–0.79. The activation energy for the cure reaction of the system was determined to be 75.1 kJ/mol by the obtained gel times at different temperatures. The steady-shear rheology test was also used to observe the viscosity change at the gel point. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1248–1256, 2000