Design of Self-Healing Supramolecular Rubbers with a Tunable Number of Chemical Cross-Links
Supramolecular rubbers incorporating a large number of physical cross-links through cooperative hydrogen bonds display high self-healing properties but limited solvent and creep resistance due to the lack of chemical cross-links. Increasing both chemical cross-links and H-bonding is therefore desirable but limited by the functionality of monomers. The present work thus devises a convergent chemical platform permitting to increase the number of chemical cross-links without changing the concentration of hydrogen-bonding groups. Starting from a single reactive prepolymer, functionalized with a defined number of hydrogen-bonding groups, a series of networks presenting different ratios of diepoxide and tetraepoxide were prepared. The curing process (controlled by 2-MI catalyst), thermomechanical behavior, and tensile properties recovery of the cured materials were investigated. Gelation state was quantified and compared to theoretical predictions. The introduction of tetrafunctional epoxide in the presence of 2-MI gave rise to gelled materials characterized by higher rigidity and strength and significantly improved creep resistance. Self-healing was observed for all materials, with 50% to 100% complete recovery in a day depending on tetraepoxide content.