Effect of block copolymer concentration and core composition on toughening epoxies

Epoxy thermosets were modified with 0–6 wt. % of poly(ethylene-alt-propylene)-b-poly(ethylene oxide) (PEP-PEO) or polystyrene-b-poly(ethylene oxide) (PS-PEO) diblock copolymers. Both polymers self-assembled into spherical micelles with PEO coronas and either a rubbery PEP or glassy PS core. The influence of the nature of the core on modulus, glass transition temperature, Tg, and critical strain energy release rate, G1c, was investigated. As block copolymer was added up to 2 wt. % loading, both block copolymers provided similar improvements in G1c. However, at 2 wt. % and above, the epoxies containing PEP-PEO diblock copolymers outperform those containing PS-PEO by approximately a factor of two. In addition, fractography of compact tension specimen surfaces revealed distinct features present on the PEP-PEO materials, which were not present on the PS-PEO-modified thermosets.