Effect of hydroxyl-terminated polyethersulfone on the phase separation of polyetherimide-modified epoxy resin

Hydroxyl-terminated polyethersulfone (HPES) is added as a second toughener to a polyetherimide (PEI)-modified epoxy resin, and phase separation initia ted by curing is studied by scanning electron microscopy (SEM), transmissio n electron microscopy (TEM), and time-resolved light scattering (TRLS). SEM shows that, by adding HPES with a higher molecular weight, phase inversion can be observed at different temperatures, and the dispersed particles sho w a bimodal size distribution. The TRLS experiment reveals that the peak sc attering vector q(m) shifts towards a smaller angle or towards a larger ang le, depending on the molecular weight of HPES added. The TEM experiment sho ws that, at an early stage of phase separation, dissimilar morphologies are observed when HPES of different molecular weights is added. The rheometry and TRLS results indicate that the morphology is pinned up by the low mobil ity of the two components before gelation or vitrification.