Mechanically robust, creep resistant and photo-stimuli-responsive elastomer vitrimer enabled by integrating boronic ester bond and carboxyl-Fe3+ complex

Abstract

Vitrimers have emerged as promising materials to balance the trade-off of the covalent crosslinking and malleability. Nevertheless, vitrimers, especially those containing exchangeable bonds with low trigger temperatures, are susceptible to creep and lose dimensional stability at service temperature, which inevitably limits their application realm. Herein, toward this dilemma, metal complexes were engineered into a rubber vitrimer network to increase the fraction of restricted segment and hinder the network rearrangement below the reprocessing temperatures. Specially, commercially available SBR was first modified with mercaptopropionic acid to implant ligand onto the rubber chains, which was subsequently crosslinked by a synthesized dithiol-containing boronic ester crosslinker. In order to exclude the adverse effect to covalent crosslinking, metal ions were introduced into the rubber vitrimer networks to form carboxyl-Fe³⁺ complex by swelling the rubber sheets into a THF solution of Fe³⁺. By incorporation of 2.1 wt% of Fe³⁺, the ultimate stress increased from 1.7 to 6.5 MPa. Meanwhile, the creep rate and creep deformation at 80 °C were reduced by 95 % and 90 %, respectively, suggesting that the sample was capable of sustaining dimensional stability under this temperature. Even so, the malleability was barely influenced as the complex was dissociated at elevated temperatures, which was demonstrated by variable temperature FTIR spectra as well as two-dimensional correlation analysis. In addition, the rubber vitrimer was ultraviolet responsive as Fe³⁺ ions are reduced to Fe²⁺ ions when exposed to UV light, leading to a promising candidate to fabricate intelligent devices.