Toughening of epoxy resins by modification with acrylic elastomers containing pendant epoxy groups

New acrylic elastomers with pendant epoxy groups were used to reduce the brittleness of bisphenol-A diglycidyl ether epoxy resin cured with p , p ′-diaminodiphenyl sulphone. The elastomers were prepared by copolymerization of butyl acrylate (BA), vinylbenzyl glycidyl ether (VBGE) and styrene (St) or acrylonitrile (AN). These terpolymers were effective for toughening of the epoxy resin system. The addition of 20 wt% of the terpolymer (74 mol% BA, 18 mol% VBGE and 8 mol% St) resulted in an 80% increase in the fracture toughness ( K 1c ) of the cured resin at the slight expense of its mechanical properties. The modified epoxy resins had two-phase morphology in which the volume fraction and average diameter of the dispersed elastomer particles were dependent on the structure and concentration of the terpolymer. The toughening mechanism is discussed in terms of the morphological and dynamic mechanical behaviour of the modified epoxy resin system.