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.
Bibliographical noteFunding Information:
The authors thank Dr. Greg D. Haugstad for assistance with scanning probe microscopy. This work was supported primarily by the MRSEC Program of the National Science Foundation under Award Number DMR-0212302 and DMR-0819885 . Support from the Dow Chemical Company is also acknowledged. Parts of this work were carried out in the Characterization Facility, University of Minnesota, a member of the NSF-funded Materials Research Facilities Network ( www.mrfn.org ) via the MRSEC program. Portions of this work were performed at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) Synchrotron Research Center located at Sector 5 of the Advanced Photon Source (Argonne, IL).
- Block copolymer