Recycling and self-healing of dynamic covalent polymer networks with a precisely tuneable crosslinking degree

Dynamic covalent polymer networks combine intrinsic reversibility with the robustness of covalent bonds, creating chemically stable materials that are responsive to external stimuli. Herein, we report a distinct approach and the first synthesis of a dynamic covalent polymer network via multi-fold nitroxide exchange reactions between defined molecular components. Upon thermal treatment of trialkoxyamine components in the presence of the trinitroxide radical species, a highly dynamic sol–gel transition can be triggered. The resulting polymer networks are elastic, highly responsive, and self-healable, show smart swelling behavior on solvent impregnation, and can be repeatedly assembled and disassembled into the sol–gel–sol phase by modulating the reaction equilibrium. Taking advantage of the dynamic and reversible alkoxyamine crosslinkages used for the network formation, thermally adjustable, precise tuning of the network structure at the molecular level is achieved. The progress of the nitroxide radical exchange reaction and tuning of the network structure can be precisely followed in situ via electron paramagnetic resonance (EPR) and fluorescence spectroscopy. This novel dynamic covalent polymeric network material with a precisely controllable and reversibly tuneable crosslinking degree, intrinsically containing favorable features, such as recyclability and self-healing, can be tailored for applications in medical implants and membrane separation or as organic energy materials.