Reactive block copolymers for modification of thermosetting epoxy

Block copolymers incorporating epoxy-reactive functionality in one block ha ve been studied as modifiers for model epoxy resins. As observed previously with nonreactive poly(ethylethylene)-b-poly-(ethylene oxide) (OP) copolyme rs, reactive poly(epoxyisoprene)-b-polybutadiene (BIxn) copolymers and poly (methyl acrylate-co-glycidyl methacrylate)-b-polyisoprene (MG-I) copolymers form ordered microstructures in blends with epoxy precursors as evidenced by small-angle X-ray scattering and transmission electron microscopy. Like OP copolymers, both types of reactive copolymer remain well-dispersed withi n the epoxy matrix during cure. Additionally, DSC and solubility studies su ggest that these copolymers can react with the curing epoxy resin to form c ovalent linkages between the copolymeric microstructures and the cross-link ed epoxy resin. The capability of these types of copolymers to template epo xy resin is proposed to arise from a combination of (1) the miscibility of one block with the epoxy components well into the curing process and (2) th e energetic barriers to nucleation and growth of copolymer-rich regions in the epoxy matrix as network formation occurs and the epoxy molecular weight diverges.