Biomimetic design of elastomeric vitrimers with unparalleled mechanical properties, improved creep resistance and retained malleability by metal–ligand coordination

Abstract

Vitrimers can undergo network reshuffling via exchange reactions, endowing the covalently crosslinked polymers with malleability and reprocessability. Elastomeric vitrimers usually suffer from poor mechanical properties and undergo undesired creep at service temperature. Thus far, the incorporation of fillers and introduction of static cross-links are feasible solutions to improve mechanical properties and creep resistance, which, however, inevitably hampers network arrangement and deteriorates the dynamic properties. Herein, we demonstrate a rational design of elastomeric vitrimers with an integration of unparalleled mechanical properties, improved creep resistance and retained malleability by engineering Zn²⁺–imidazole complexes into the network. Specifically, commercially available styrene-butadiene rubber (SBR) grafted with 2-(2-benzimidazolyl)ethanethiol is covalently crosslinked with the dithiol-containing boronic ester cross-linker through thiol-ene “click” chemistry reaction. Afterwards, Zn²⁺–imidazole complexes are introduced and lead to the formation of a micro-phase separated structure. Zn²⁺–imidazole complexes can function as sacrificial units through reversible breaking and reforming events, leading to significant enhancements on the modulus, strength and toughness while maintaining the extensibility of the networks. In addition, the creep resistance at service temperature is improved as the Zn²⁺–imidazole complexes can act as cross-links to restrict segment mobility, whereas, the network arrangement at elevated temperatures is not affected due to the dissociation of Zn²⁺–imidazole complexes, allowing the networks to be reshaped and recycled.