A Look Into the Deformation Events in Block Copolymer Modified Epoxies: A SAXS Perspective

Epoxy resins are an important class of thermosetting polymers. Their high crosslink density provides stiffness, thermal stability and solvent resistance, but also renders these materials very brittle. Addition of small amounts (~5% wt.) of block copolymers (BCPs) significantly increase the facture resistance of epoxy resins. The observed increase in toughness is correlated with the formation of BCP micelles. However, a full description of the mechanisms leading to increased toughness is not available. Here we report the use of simultaneous small angle x-ray scattering (SAXS) and tensile experiments to connect local deformation processes of the BCP micelles to the macroscopic mechanical response of BCP modified epoxies. With this technique we followed the deformation events of rubbery and glassy core BCP micelles. We show that the rubbery core micelles are prone to cavitation and dialation, while the glassy core micelles deforms with constant volume. Finally, we discuss how the onset of cavitation is strongly affected by important characteristics of the epoxy network: its crosslink density and backbone flexibility.