Self-healing of cross-linked PU via dual-dynamic covalent bonds of a Schiff base from cystine and vanillin

A Schiff base containing dual-dynamic covalent bonds synthesized from the biomaterials, cystine and vanillin, showed excellent reversibility under external stimuli by metatheses. The synthesized Schiff base containing imine and disulfide bonds was mixed with 1,4-butanediol (BD) to ensure miscibility with polyurethane (PU) prepolymers and then employed as a chain extender to introduce self-healing and recyclability to crosslinked PU (CPU). Compared with CPUs containing only one type of dynamic covalent bond such as imine or disulfide group, the PU crosslinked with the Schiff base (SPU) showed excellent self-healing and recyclability with lower activation energy for stress relaxation behavior attributable to the synergy of the dual-dynamic metatheses of the imine and disulfide bonds. Furthermore, the developed SPU showed dual-responsive self-healing by heat and UV irradiation. This Schiff base derived from biomaterials is expected to be useful for the design of CPU for coatings, adhesives, and matrix polymers of composites that require self-healing and recyclability as well as sustainability. (c) 2019 The Authors. Published by Elsevier Ltd.