Rheological behaviors and structural transitions in a polyethersulfone-modified epoxy system during phase separation

The rheological behaviors and gelation transitions in a polyethersulfone (PES)-modified epoxy system during phase separation were studied by rheometry, time-resolved light scattering, and differential scanning calorimetry. Two separate structural transitions in the curing process of the blend were identified as the first one because of phase separation and the second one related to cross-linking reaction of epoxy resin. Both the times of the two structural transition at different temperatures could be described well by the Arrhenius type equation. The complex viscosity exhibits an exponential growing process during phase separation at various temperatures, correlating to the light-scattering results. The exponential behavior of complex viscosity could be attributed to the viscoelastic flow of epoxy-rich escaping from PES-rich during phase separation process.