Understanding molecular and macroscopic relaxation processes in model epoxy resins : theoretical and practical aspects

Abstract

In the previous phase o f this research project completely phase separated and partially phase separated bimodal epoxy resins were prepared by incorporating a 22,500 weight average molecular weight advanced epoxy resin into a DGEBA /DADPS epoxy resin system during the cure process. In the as cured condition, these bimodal epoxy resin exhibited an enhancement o f fracture toughness properties that was found to be dependent on the phase morphology o f the system. Since these bimodal epoxy resins were cured at temperatures in which traditional DGEBA/DADPS epoxy resins exhibit inferior m echanical properties and the fracture toughness in the com pletely phase separated system was found to be related to restricted mobility in the beta relaxation region, a fundamental study was undertaken to elucidate the properties relevant to defining the short term and long term mechanical behavior o f these materials. In this report the effects o f reaction kinetics, m iscibility o f reactants and cured product, dynamic mechanical properties, physical aging, degradation at elevated temperatures, and the long term fracture properties o f these model epoxy resins are investigated.