Effect of cross-link density on modification of epoxy resins with reactive acrylic elastomers

Abstract

The effect of cross-link density on the toughness of modified resins was investigated for modification of epoxy resins with acrylic elastomers with pendant epoxy groups. The elastomers were prepared by terpolymerization of butyl acrylate (BA), glycidyl methacrylate (GMA) and acrylonitrile (AN). The cross-link density of the epoxy matrix was controlled using hybrid hardeners composed of p, p′-diaminodiphenyl sulphone (DDS) as a primary diamine and p, p′-( N, N′-dimethyl)-diaminodiphenyl sulphone (MDS) as a secondary diamine. The terpolymers were effective as modifiers for toughening of difunctional epoxy resins (bisphenol A diglycidyl ether). The addition of 20 wt% of the terpolymer (62 mol% BA, 25 mol% GMA and 13 mol% AN, M n 7900 ) led to a 100% increase in the fractural toughness of the resin cured with the hybrid hardener (DDS/MDS, 48:52 mol ratio, 65:35 NH ratio). The lower the cross-link density, the larger was the fracture toughness and the lower was the glass transition temperature. On the other hand, the terpolymers were less effective in the modification of trifunctional epoxy resins of higher cross-link density (triglycidyl aminocresol) even when using the hybrid hardener (DDS/MDS, 48:52 mol ratio). Both modified systems afforded cured resins with two-phase morphologies. The toughening mechanism is discussed in terms of the morphological and dynamic mechanical behaviours of the modified epoxy resin systems. It is concluded that the ductility of the epoxy matrix contributes greatly to toughening of epoxy resins with acrylic elastomers.