(718a) Studying the Toughening Mechanism of Mussel-Inspired Iron-Catechol Complexes in Epoxy Networks

It is challenging to synthesize covalent polymer networks which are both stiff and extensible. One strategy to overcome this challenge is to incorporate both permanent covalent bonds and reversible bonds of various chemistries into the same network. The marine mussel is known to apply this strategy via reversible iron-catechol coordination complexes in its byssal threads which yields a highly extensible and strong material. In this work, the same iron-catechol complexes found in the mussel system are incorporated into a polyethylene glycol epoxy network. The resulting hybrid network is orders-of-magnitude stiffer than its iron-free equivalent (as measured by a uniaxial tensiometer) and can reversibly dissipate energy upon cyclic loading. Small-angle x-ray scattering suggests that the iron-catechol complexes form ionomeric nanodomains within the network which may further restrict chain mobility and therefore enhance the effect of the additional reversible cross-links. The ratio of constituent monomers was varied to dilute the network’s catechol content and study the role of the iron-complexes and nanodomains in the network’s mechanical properties. The effects of exposing the network to humidity and oxidative environments were also explored and were respectively shown to reversibly and irreversibly reduce the network’s ultimate tensile strength. This work demonstrates that iron-catechol complexes can be used to enhance the mechanical properties of polymer networks, however the mechanism depends heavily on environmental conditions and the network’s nanostructure.