Dynamic imidazole-urea bonds for designing recyclable and crosslinked poly(imidazole-urea)

Covalent adaptable network (CAN) with the ability of structural rearrangement has attracted great attentions in recent years because it breaks the limitations in reprocessability and recyclability of traditional thermosetting polymers. Developing catalyst-free dynamic chemistry that proceeded in mild condition would make significant advances in the field of CAN and hold great promise for real applications. Here, we report a new class of highly dynamic imidazole-urea bonds for developing dynamically crosslinked poly (imidazole-urea) (PIU). The reversible reaction and the reaction kinetics between different imidazoles and isocyanate were first studied by model compounds. PIUs with varied crosslinking structures were then constructed from biobased histamine and commercially available isocyanates. Rheological and stress relaxation analysis revealed the rearrangement ability of PIUs at elevated temperature, while thermogravimetric and tensile tests showed their good thermal stability and mechanical properties. The reprocessed PIUs also demonstrated high recovery efficiency of mechanical properties after several cycles of reprocessing. It is expected that this study could broaden the scope of imidazole compounds for novel dynamic polymers.