Phase separation of poly(ether sulfone imide) modified epoxy resins

Amine terminated poly(ether sulfone imide) (PESI) with various imide and ethersulfone contents but similar polymer molecular weights were blended with diglycidyletherbisphenol-A (DGEBA) and cured with diaminodiphenylsulfone (DDS). The imide group, a tertiary amine, is a catalyst of the curing reaction of DGEBA with DDS, but it is poorly compatible with uncured epoxy resin. The ethersulfone group is not a catalyst of the curing reaction of DGEBA with DDS, but it has a similar chemical structure as DDS and is compatible with epoxy resin while it is at a low degree of curing. Since PESIs used in this study had similar molecular weights, increasing imide content of PESI would reduce ethersulfone content. The influence of imide and ethersulfone contents of PESI on the phase separation and curing reaction of DGEBA/DDS/PESI blend was investigated using differential scanning calorimetry (DSC), time-resolved light scattering (TRLS), and polarized optical microscopy (POM). Though the imide group has a catalysis effect on the curing reaction of DGEBA with DDS, however, its poor compatibility with epoxy resin retards the curing reaction. Our experimental results revealed the morphology of the cured blends and the curing behavior was a compromise result of catalysis and compatibility of PESI with epoxy resin.