Weak bonds are well-known to construct soft materials. Elaborating molecule-level self-assembly via supramolecular engineering could generate performance materials that exhibit high strength at mild temperatures. However, the entropy penalty of assembled materials, meanwhile, compromises robustness at elevated temperatures. Herein, we report that simply replacing two carbons with disulfide bonds in poly(urea)s enables unprecedented structural reconfigurability without trading off material robustness. Introducing disulfide bonds maintains the ordered urea-based H-bond assembly in bulk polymers while simultaneously suppressing secondary crystallization of these H-bonded arrays and offering secondary H-bonding sites by forming S─S·H─N interactions. This two-atom structural change revitalizes semicrystalline homopoly(urea) materials by allowing chain mobility and reconfiguration below melting temperatures to enable thermoplastic-like (re)processability and thermoset-like robustness, including more than 2-gigapascal storage modulus, a broad creep-resistant temperature range (up to 150°C), ceramic-like hardness, and resistance to common solvents. Furthermore, these materials exhibit acid-catalyzed depolymerization potential, enabling closed-loop recyclability.
Zong et al. (Wed,) studied this question.