Oxidation-Driven Shape-Shifting Rubber Composites by Metal–Polyphenol Bonds

Shape-shifting materials have attracted a lot of attention owing to important roles of geometric shapes in engineering applications. But it is still a challenge to explore simple and effective strategies to shift their shapes in association with time. Herein, we have reported a simple method to prepare shape-shifting composites by introducing metal–polyphenol coordination bonds to cross-link rubber. As special stimuli, oxidation stimuli were used to trigger cross-linking network variations of rubber composites through self-oxidation reaction of polyphenols. As the oxidation time increased, the single cross-linking network in rubber composites transited to hybrid networks composed of covalent and coordination ones. Accordingly, oxidation allowed temporal tuning of material properties, including chemical composition, morphology, glassy temperature, mechanical properties, and elasticity. Shape-memory performance showed that the shape recovery speed increased with oxidation time in the range of 20 days of oxidation owing to the increase of covalent cross-linking bonds. We demonstrated that the unique attribute is beneficial in sequent shape-memory products after orderly assembling the oxidized samples. Therefore, the metal–polyphenol cross-linking networks are possibly important to fabricate shape-shifting rubber composites for their time-dependent applications, such as 4D printing technology.