Toughening Rubber by In Situ Construction of Hierarchical Coordination Complexes with a Sulfur-Based Ionomer

Programming energy-dissipating units into polymers is an effective method to improve the toughness; however, the state-of-art approaches usually involve complicated chemistry manipulation and multistep process. In this contribution, we report a brand-new way to toughen styrene-butadiene rubber (SBR) by incorporating a sulfur-based ionomer to construct hierarchical coordination complexes. Specifically, the ionomer P(TA-S)/Fe containing polysulfide backbones and iron-carboxylate complexes was synthesized through the copolymerization of thioctic acid and sulfur, followed by introducing ferric chloride. Due to the reaction between polysulfide fragments in P(TA-S)/Fe and SBR, the incorporation of P(TA-S)/Fe enabled the chemical cross-linking of SBR and grafting of iron-carboxylate complexes onto SBR chains. The grafted iron-carboxylate complexes aggregated and formed a phase separate structure within SBR, which provided a multilevel energy-dissipating mechanism and consequently led to an integration of enhanced ultimate strength, modulus, and fracture toughness of SBR.