Phase separation in epoxy resins containing polyethersulphone

Scanning electron microscopy and dynamic mechanical spectroscopy have been used to study phase separation of dissolved polyethersulphone (PES) from trifunctional and tetrafunctional epoxy resins during curing. No phase separation was observed at high concentrations of the tetrafunctional resin. Observations of nodules on fracture surfaces, and of multiple peaks in the dynamic mechanical spectra provided evidence for a separate, crosslinked, PES-rich phase in the remaining materials. Despite the variety of morphologies obtained in mixtures of PES with different hardeners and resins, modulus and fracture toughness showed little dependence upon composition.