Curing Kinetics and Phase Separation of Epoxy System Modified With Polyetherimide

ABSTRACT The present study focuses on the curing process of epoxy oligomer modified with polyetherimide. The rheological behavior and phase separation in the system have been the subject of detailed study. The findings of the present study demonstrate that the incorporation of polyetherimide (PEI) into epoxy binders can enhance their pot‐life by a duration ranging from 10 to 26 min, depending on the composition of the cured material and the temperature at which the experiment is conducted. At the same time the limit of conversion is reduced by 0.2 relative to the unmodified system. The activation energy of the initial stage of curing decreases by 7–14 kJ/mol at a PEI content of 10 parts by weight (p.b.w.) and further increases with higher modifier content. It was established that an elevated thermoplastic content resulted in an earlier onset of phase separation in the epoxy‐PEI system during the curing process. This results in the formation of a matrix‐dispersion type structure, with PEI enriched particle size not exceeding 1.5 μm.