(672c) Enhancing Epoxy Network Toughness and Recoverability with Mussel-Inspired Catechol-Iron Crosslinks

Iron-catechol metal-ligand coordination bonds have previously been shown to impart both hardness and strength to the marine mussel byssal thread while simultaneously maintaining high extensibility, thus creating an extremely tough material with excellent energy-dissipation properties. These properties show a clear deviation from the commonly accepted trade-off between strength and extensibility observed in typical industrial polymers, making them desirable properties for polymer coatings and adhesives. Though these properties have been successfully realized in low-modulus hydrogel networks, this work aims to demonstrate that high-elastic modulus (~100 MPa), high-strain (~100-200%) materials can also be synthesized using a similar synthetic approach in epoxy networks. Low-cross-link density poly(ethylene glycol)/epoxy networks were synthesized with pendant catechol groups and subsequently swollen and treated in iron(III)-containing solutions at both low and high pH. The treated networks were then dried and chemically verified using various spectroscopies, and the mechanical properties were tested under tension. Larger than an order-of-magnitude increase in elastic modulus was observed with less than 25% decrease in extensibility as compared to the untreated samples. Due to the reversible nature of the iron-catechol coordination bonds, the networks also demonstrate the ability to quickly recover their initial mechanical properties after plastically deforming during cyclic tensile tests. Therefore, it is clear that the incorporation of iron-catechol coordination bonds in dry polymer materials may be a synthetic strategy for greatly increasing material strength without sacrificing extensibility.

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