Mechanically robust, exceptionally recyclable and shape memory cross-linked network based on reversible dynamic urea bonds

Abstract

Using dynamic covalent bonds to construct dynamic polymer materials has been attracting interest to thrive the smart, responsive and adaptive polymeric materials. However, it is a challenge to design mechanically robust and exceptionally recyclable dynamic polymeric materials. Herein, we integrate dynamic urea bonds based on a commercial raw piperazine monomer into the molecular structure of hindered thermosetting polyureas (HTPUs) elastomers. The piperazine monomer contains bulk substituents of two methyl groups and an asymmetric alicyclic structure, which can endow the synthesized HTPUs elastomers with excellent mechanical properties and exceptional reprocessability. Especially, after multiple rounds of reprocessing, the breaking strength and elongation at break of the recycled HTPUs elastomers are equivalent to those of the original elastomers and can still maintain superhigh values of 24.15 MPa and 1295.31%, respectively, which are still superior to the commercial high-impact elastomers, including polythene and polypropylene, showing exceptional reprocessability and recyclability. Additionally, the synthetic HTPUs elastomers have outstanding 3D permanent shape reconfigurability via topological rearrangements, which can solve the intrinsic problem of the inability to permanently reshape the original shape of traditional shape-memory polymers into another shape. Integration of conventional elastic shape memory and 3D permanent shape reconfiguration into one network can enormously broaden the variety and complexity of shape changes. The designed strategy provides a new approach to recycle mechanically robust thermosetting polymers and apply these polymers in high value functions and industrial applications.