Dynamic covalent polymers: Reorganizable polymers with dynamic covalent bonds

The recent research on dynamic covalent polymers is reviewed. These polymers exhibit dynamic features originating in the reversibility of dynamic covalent bonds. The main body of the review is presented in four sections: (i) utilization of dynamic covalent bonds in reactive polymer blends, (ii) ring–chain equilibrium based on dynamic covalent bonds, (iii) reorganizable polymers and polymeric systems with dynamic covalent bonds, and (iv) dynamic smart polymer materials. Unlike conventional polymers that are irreversibly formed, dynamic covalent polymers can reform their structures and constitutions under appropriate conditions, even after polymerization. Utilization of dynamic covalent bonds is seen in research concerning polymerization controls and polymer blends. In addition, reorganizable macromolecules specially programmed to exhibit dynamic features have recently been highlighted in line with increased understanding of dynamic phenomena through reversible formation of non-covalent bonds. They include various dynamic covalent bonds typified by CN bonds in imine derivatives and CO bonds in alkoxyamine moieties, and are not only converted into macromolecules with different constitutions or gels, but also exhibit discriminating properties attributed to the reversibility of dynamic covalent bonds by adequate external stimuli, such as heating and the addition of a catalyst. The trend of dynamic covalent polymers is directed to intelligent systems using equilibrium under reorganization processes and stimulus-responsive polymeric materials based on bond-reformation.