Compatibilized, Segmented Liquid Rubbers as Epoxy-Toughening Agents

Abstract

Novel hybrid composites and advanced structural materials, such as structural adhesives and fiber-metal laminates that are resistant to high-velocity impact, are based on epoxy resins toughened with compatibilized, segmented, reactive liquid rubbers. Upon cure, interpenetrating networks containing dispersed rubber micro- and nanoparticles are formed. Morphological and mechanical properties are controlled by liquid-rubber molecular architectures, especially by the balance of segments that are either compatible or incompatible with the epoxy matrix. Novel poly(ε-caprolactone)-block-poly(dimethylsiloxane)-block-poly(ε-caprolactone) liquid rubbers improve the toughness of silica-filled epoxy resins without sacrificing stiffness. Blends of compatibilized liquid rubbers, such as bisphenol-terminated segmented polyetherurethanes with epoxy-terminated nitrile rubber, possess rubber-blend microphases that account for unusual property synergisms, namely, substantially improved static and high-velocity impact resistance, high T-peel strength combined with high lap shear strength, excellent adhesion, and improved fatigue resistance.