Reactive Block Copolymers for Modification of Thermosetting Epoxy

Block copolymers incorporating epoxy-reactive functionality in one block have been studied as modifiers for model epoxy resins. As observed previously with nonreactive poly(ethylethylene)-b-poly(ethylene oxide) (OP) copolymers, 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 within the epoxy matrix during cure. Additionally, DSC and solubility studies suggest that these copolymers can react with the curing epoxy resin to form covalent linkages between the copolymeric microstructures and the cross-linked epoxy resin. The capability of these types of copolymers to template epoxy 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) the energetic barriers to nucleation and growth of copolymer-rich regions in the epoxy matrix as network formation occurs and the epoxy molecular weight diverges.