Phase‐Separated Structures and Fracture Toughness of Epoxy/Imide‐Terminated Reactive Oligomer With Flexible Chain

The phase‐separated structures and fracture toughness of epoxy/reactive oligomer blends were investigated. Imide groups were introduced into nonpolar reactive oligomers, enabling the design of an imide‐terminated reactive oligomer (AO3636DIDA) that exhibited good compatibility with biphenyl‐type epoxy resins. The epoxy blends cured with a phenol novolac curing agent formed phase‐separated structures during the curing process. Compared with the cured epoxy blends containing reactive oligomers without imide groups, the cured epoxy/imide‐containing reactive oligomer blends exhibited fine phase‐separated structures that were independent of both the pre‐curing temperature and the oligomer content (up to 15 wt%). In addition, the cured epoxy/imide‐containing reactive oligomer blends exhibited a maximum 110% increase in fracture toughness compared with the unmodified cured epoxy resin.