Reorganizable Chemical Polymer Gels Based on Dynamic Covalent Exchange and Controlled Monomer Insertion

Covalently networked polymer gels were developed with two notable functionalities: de-cross-linking by dynamic covalent exchange based on a radical crossover reaction and insertion of a monomer into the cross-linkers. The network polymer gels were synthesized by free-radical copolymerization of styrene and a bifunctional monomer with an alkoxyamine linker that has two capabilities to exchange with other alkoxyamine derivatives in the radical process and to polymerize styrene in a controlled manner. Three types of network polymers with different cross-linking densities were obtained by changing the ratio of the bifunctional monomer to styrene. The de-cross-linking reaction was carried out by heating the network polymers with excessive alkoxyamine compound in anisole, and it was made clear that the de-cross-linking behavior strongly depended on the cross-linking densities. The insertion of styrene into the alkoxyamine units at the cross-linking points was also performed by heating the network polymers swollen with styrene and anisole, and it was revealed that the mesh sizes grew larger by the insertion of styrene into their skeleton and that the cross-linking density decreased as the reaction proceeded. The variation of the network structures in these reactions was successfully evaluated by small-angle X-ray scattering and dynamic viscoelasticity measurements.