Doubly-dynamic-covalent polymers composed of oxime and oxanorbornene links

Two sets of reversible covalent linkages distributed in series along a polymer backbone were used to prepare a new class of doubly-dynamic-covalent polymers capable of reversibly dissociating via two distinct pathways. These self-repairable linear polymers were prepared via step-growth Diels–Alder polymerization of an AB monomer that contained furfuryl- and maleimido groups linked by an oxime bond. Both the oxime and oxanorbornene links lent orthogonally reversible character to the polymer backbone. The sequentially distributed oxime bonds in the polymer were capable of dynamic oxime exchange in the presence of a competitive monofunctional alkoxyamine under acidic conditions, while the oxanorbornene linkages were susceptible to cleavage via retro-Diels–Alder reactions at elevated temperatures and recombination upon cooling. The self-healing or reversible nature of the dynamic-covalent oxime bonds and oxanorbornene links has potential for designing stimuli-responsive self-repairable materials for sensors and drug delivery applications.