TOUGHENING OF AROMATIC DIAMINE-CURED EPOXY-RESINS BY MODIFICATION WITH N-PHENYLMALEIMIDE-STYRENE-P-HYDROXYSTYRENE TERPOLYMERS

N-phenylmaleimide-styrene-p-hydroxystyrene terpolymers (PMSH), contain ing pendant p-hydroxyphenyl groups as functionalities, were prepared a nd used to improve the toughness of bisphenol-A diglycidyl ether epoxy resin cured with p,p'-diaminodiphenyl sulphone. The terpolymers were effective as modifiers for toughening the epoxy resin. When using more than 10 wt% of PMSH with <3.0 mol.% p-hydroxystyrene (HSt) units, the fracture toughness (K-IC) for the modified resins increased > 100% wi th a medium loss of flexural strength and with a retention in flexural modulus and the glass transition temperature. For example, inclusion of 12.5 wt% of PMSH (1.0 mol.% HSt unit, M(w) 291,000) led to a 130% i ncrease in K-IC. The most effective modification for the modified rein s could be attained because of the co-continuous structure of the modi fied resins. The toughening mechanism is discussed in terms of the mor phological behaviors of the modified expoxy resin systems.