Toughening tetrafunctional epoxy resins using polyetherimide

Toughened epoxy resins have been prepared by dissolving polyetherimide (PEI) in a tetraglycidyl-4,4′-diaminodiphenyl methane (TGDDM) based resin with 30 p.h.r. diaminodiphenyl sulphone (DDS) as curing agent. The polyetherimide forms a separate phase, with a dynamic loss peak which varies between 200 and 212°C. The loss peak of the resin occurs at about 265°C. Three-point bend tests show a linear increase in K IC with PEI content, from 0.5MPa√m in the parent resin to 1.42MPa√m at 25 p.h.r. of PEI. Young's modulus at 23°C shows a modest reduction from 3.6 to 3.5 GPa over the same composition range.