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.
Highlights
Constructing responsive and adaptive materials by dynamic covalent bonds is an attractive strategy in material design
We present the reversible pyrazole–urea bonds (PzUBs), which are applied for the design of a series of mechanically robust dynamic polymers, poly(pyrazole–ureas) (PPzUs)
We first investigated the addition reaction between octyl isocyanate 1b and 4-methylpyrazole 1c (Fig. 1b), whose rate was monitored through the change of NCO infrared absorption
Summary
Constructing responsive and adaptive materials by dynamic covalent bonds is an attractive strategy in material design. Great efforts have been made to create complex, smart, and adaptive polymeric materials that allow access to topological/constitutional structure transformation[4], controlled assembly[5], shape memory[6,7], self-healing, and recyclability[8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33], to name a few In this context, the library of dynamic polymers has extended rapidly, it remains a challenge to design mechanically robust dynamic polymers with high strength, extensionality, and malleability. The crystallization behavior of PPzUs offers substantial advantages in terms of strength, toughness, and solvent resistance in contrast to the amorphous dynamic polymers
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