CHARACTERIZATION OF NETWORK STRUCTURES OF MULTIPHASE EPOXY RESINS BY DYNAMIC MECHANICAL ANALYSIS.

Dynamic mechanical analysis (DMA) has been used to elucidate the structure of a high temperature curing epoxy resin modified by reactive styrene, whose incorporation with the epoxy improves the processability and, preferably, also the toughness through modification of morphological features of the cured resin. Phase separation is examined using the DMA, which shows that there are two major phases in the modified epoxy resin. Tg characterization indicates that the epoxy-rich phase is plasticized by the polystyrene component. However, a broadened polystyrene relaxation peak suggests that partial miscibility may also result in a series of minor phases intermediate between the two major phases. Additionally, the dynamic mechanical properties in the rubbery region were used to estimate the crosslinking densities of the modified and basic epoxy resins. The development of a polystyrene-rich phase during epoxy conversion is found to be influenced by the amount of catalyst present, as well as the temperature of the reaction i. e. , both by kinetic and thermodynamic factors.