EFFECT OF CROSS-LINK DENSITY ON MODIFICATION OF EPOXY-RESINS BY N-PHENYLMALEIMIDE STYRENE COPOLYMERS

The effect of cross-link density on the toughening of modified resins was investigated for the modification of epoxy resins with N-phenylmal eimide-styrene alternating copolymers (PMS). The cross-link density of the epoxy matrix was controlled by a combination of two kinds of epox y resins [diglycidyl ether of bisphenol-A (DGEBA) or triglycidyl amino cresol (TGAC)] and hybrid hardeners composed of p,p'-diaminodiphenyl s ulphone (DDS) and p,p'-(N,N'-dimethyl)-diaminodiphenyl sulphone (MDS). The addition of 10 wt% of PMS (M(w)BAR 214,000) led to 120% increase in the fracture toughness (K(IC)) of the DGEBA resin cured with the hy brid hardener (DDS: MDS, 67: 33 mol ratio). On addition of 15 wt% of P MS (M(w)BAR 214,000), K(IC) for the modified resin increased 110% in t he TGAC/hybrid hardener (DDS: MDS, 67: 33 mol ratio) system. Morpholog ies of the modified resins depended on PMS molecular weight and concen tration, and the cross-link density of the matrix. The toughening of e poxies could be explained by the cocontinuous phase structure in every case.