Dynamic multiphase semi-crystalline polymers based on thermally reversible pyrazole-urea bonds

Abstract

Constructing responsive and adaptive materials by dynamic covalent bonds is an attractive strategy in material design. Here, we present a kind of dynamic covalent polyureas which can be prepared from the highly efficient polyaddition reaction of pyrazoles and diisocyanates at ambient temperature in the absence of a catalyst. Owing to multiphase structural design, poly(pyrazole-ureas) (PPzUs) show excellent mechanical properties and unique crystallization behavior. Besides, the crosslinked PPzUs can be successfully recycled upon heating (~130 °C) and the molecular-level blending of polyurea and polyurethane is realized. Theoretical studies prove that the reversibility of pyrazole-urea bonds (PzUBs) arises from the unique aromatic nature of pyrazole and the N-assisting intramolecular hydrogen transfer process. The PzUBs could further broaden the scope of dynamic covalent bonds and are very promising in the fields of dynamic materials. Dynamic polymer materials with reversible covalent bonds can reorganize their macromolecular architectures, and thus produce a macroscopic response to the environment. Here, the authors show dynamic covalent polyureas formed by a polyaddition reaction between pyrazoles and diisocyanates at ambient temperature in the absence of a catalyst.