TOUGHENING OF EPOXY-RESINS BY N-PHENYLMALEIMIDE-N-CYCLOHEXYLMALEIMIDESTYRENE TERPOLYMERS

N-Phenylmaleimide (PMI)-N-cyclohexylmaleimide (CMI)-styrene (St) terpo lymers were used to improve the toughness of bisphenol-A diglycidyl et her epoxy resin cured with p,p'-diaminodiphenyl sulfone (DDS). The ter polymers were effective as modifiers for toughening of the epoxy resin system. The most suitable compositions for the modification of the ep oxy resin were inclusion of 10 wt % of the terpolymer (45 mol % PMI, 5 mol % CMI, and 50 mol % St units) with M(w) higher than 247,000, whic h led to ca. a 140% increase in the fracture toughness (K(IC)) of the cured resin with a medium expense of mechanical properties. The glass transition temperatures of the modified resins were equal to or higher than that of the parent epoxy resin. The morphologies of the modified resins were dependent on the terpolymer molecular weight and concentr ation. On addition of 5 wt % of the terpolymer (M(w) 400,000), the mod ified resins had two-phase morphologies and the terpolymer-rich disper sed particles in the epoxy matrix. On addition of more than 8 wt % of the terpolymer, the morphologies of the cured resins changed drastical ly and showed a tendency to form cocontinuous phases. The toughening m echanism was discussed in terms of the morphological behaviors of the modified epoxy resin systems.