Reversibility of solid state radical reactions in thermally remendable polymers with C–ON bonds

The C–ON covalent bond with thermally responsive function opens a new avenue to prepare remendable polymers. Carbon-centered radicals and oxygen-centered nitroxide free radicals produced by homolytic cleavage of C–ON bonds at healing temperature synchronously reorganize to form cross-linked networks, offering effective damage repairing characteristics without losing integrity and load bearing ability of the material even above Tg. To gain a deeper understanding of the mechanisms, thermally remendable two-component polymer blends carrying two types of C–ON bonds in the side chains were synthesized. With the aid of small molecule mimetics, intermolecular reactions involved in thermal reversibility of the polymer blends and self-healing capability are analyzed. It was found that crossover reaction between carbon-centered radicals and oxygen-centered nitroxide radicals is necessary, but the possibility of the irreversible combination of carbon-centered radicals should be eliminated. Polymer solid hinders diffusion of carbon-centered radicals so that the unwanted secondary reaction is depressed even though complete recombination of the cleft C–ON bond is also somewhat blocked. Basically, reversibility and multiple self-healing behaviors of the synthesized polymer blends are satisfactory in addition to the expanded healing temperature range. These results are believed to favor materials design and improve crack healing performance based on efficient bond fission and radical recombination.