Effect of cross-link density on modification of epoxy resins by N-phenylmaleimide-styrene copolymers

Abstract

The effect of cross-link density on the toughening of modified resins was investigated for the modification of epoxy resins with N-phenylmaleimide-styrene alternating copolymers (PMS). The cross-link density of the epoxy matrix was controlled by a combination of two kinds of epoxy resins [diglycidyl ether of bisphenol-A (DGEBA) or triglycidyl aminocresol (TGAC)] and hybrid hardeners composed of p, p′-diaminodiphenyl sulphone (DDS) and p, p′-( N, N′-dimethyl)-diaminodiphenyl sulphone (MDS). The addition of 10 wt% of PMS ( M w 214,000 ) led to 120% increase in the fracture toughness ( K 1C) of the DGEBA resin cured with the hybrid hardener (DDS: MDS, 67:33 mol ratio). On addition of 15 wt% of PMS ( M w 214,000 ), K 1C for the modified resin increased 110% in the TGAC/hybrid hardener (DDS: MDS, 67:33 mol ratio) system. Morphologies of the modified resins depended on PMS molecular weight and concentration, and the cross-link density of the matrix. The toughening of epoxies could be explained by the cocontinuous phase structure in every case.