Covalent adaptive networks with repairable, reprocessable, reconfigurable, recyclable, and re-adhesive (5R) performance via dynamic isocyanate chemistry

Polymer materials with covalent adaptive networks (CANs) structures have attracted considerable attention in recent years due to their excellent repairable, reprocessable, reconfigurable, recyclable, and re-adhesive (5R) performance. Many types of CANs based on reversible dissociation or association reactions have been developed. Of these, CANs via dynamic isocyanate chemistry have made significant progress on the creation of smart polyurethane (PU) and polyurea (PUR) materials. Herein, we provide a comprehensive review on the recent development of CANs via dynamic isocyanate chemistry. First, we provide a brief introduction of dynamic isocyanate chemistry. Second, several categories of dynamic isocyanate chemistry (and the mechanism behind them) are discussed in detail. Third, we focus on the characterization of CANs via dynamic isocyanate chemistry by physical and chemical approaches. Fourth, we focus on novel types of "smart" polymer materials containing a CANs structure with 5R properties via dynamic isocyanate chemistry. The influence of different categories of dynamic isocyanate chemistry on the stress relaxation and 5R performance are summarized in detail in this part. The advantages and disadvantages of different types of dynamic isocyanate chemistry for 5R applications are also discussed. Finally, conclusions and the outlook on the development and challenges of CANs via dynamic isocyanate chemistry are provided.