Highly stretchable and strong poly(butylene maleate) elastomers via metal–ligand interactions

The search for advanced elastomers with simultaneously high strength, high stretchability and reprocessability remains a challenging task. Herein, we report an innovative method to prepare high-performance yet reprocessable poly(butylene maleate) (PBM) elastomers by forming dynamic metal–ligand (M–L) crosslinks among PBM chains. 2-Pyrazine ethanethiol, a commercially available food flavor, was used to introduce pyrazine ligands on PBM chains by the thiol–ene click reaction. A series of metal salts with different metal ion valences, counteranions and metal types were used to form metal–pyrazine interactions, showing that all three factors affect the M–L bond strength and thus the mechanical behavior of the crosslinked PBM elastomers. A tensile strength as high as 4 MPa and elongation at break up to 1630% were achieved for the Fe(BF4)2-crosslinked PBM elastomer, which were 1 and 22 times better than those of a covalently crosslinked PBM elastomer, and the dynamically crosslinked PBM elastomer can be reprocessed at 100 °C by hot pressing. This excellent recyclability was attributed to the dynamic nature of M–L bonds. During tensile testing, some of the M–L bonds were reversibly broken and reformed to release two types of coiled segments and enable the chain sliding, resulting in high extensibility; in the meantime, the M–L interactions and the network structure were optimized when the molecular chains were gradually oriented along the pulling direction, ensuring high strength. The designed M–L crosslinked PBMs are promising candidates for advanced elastomers with highly tunable mechanical properties.