Toughening of epoxy resins by N-phenylmaleimide-styrene copolymers

Abstract

N-Phenylmaleimide (PMI)-styrene (St) alternating copolymers were used to improve the toughness of bisphenol-A diglycidyl ether epoxy resin cured with p, p′-diaminodiphenyl sulphone (DDS). The most suitable composition for the modification was inclusion of 10 wt% of the copolymer ( M w 345,000 ) which led to a 130% increase in the fracture toughness ( K IC) of the cured resin with a medium decrease of its 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 copolymer molecular weight and concentration. On addition of up to 7 wt% of the copolymer ( M w 345,000 ) the modified resins had two-phase morphologies with the copolymer-rich dispersed particles in the epoxy matrix. On addition of 8 wt% of the copolymer, the morphologies of the cured resins changed drastically and showed a tendency to form co-continuous phases. The toughening mechanism is discussed in terms of the morphological characteristics of the modified epoxy resin systems.