Poly(ethylene terephthalate), PET, dissolved in diglycidyl ether of bisphenol-A epoxy resins, DGEBA, is used as a toughening modifier. Two DGEBA resins in the presence of PET have been cured with the aid of diaminodiphenyl sulfone, DDS, in stoichiometric proportion. The curing process of the system DGEBA with DDS, in the presence of PET in particular, is monitored applying differential scanning calorimetry, DSC, in isothermal mode. The curing data are used to estimate the temperature regime in a microwave, MW, cavity. Physical confirmations for obtaining sub-micro phase separated DGEBA-DDS-PET composites and, in turn, for efficient modifying of the epoxy phase, have been discussed. (C) 2014 Elsevier B.V. All rights reserved.