Calix[6]arene-Based Interlocked Inverse Vulcanizate Enabling Network-Interface Cooperative Reinforcement in Natural Rubber/Carbon Black Composites.

Conventional sulfur vulcanization provides practical cross-linking for unsaturated rubbers but struggles to simultaneously improve tear resistance, impact durability, processing stability, and aging performance through a simple and scalable strategy. Herein, we report a calix[6]arene-mediated inverse vulcanization approach to engineer mechanically interlocked polysulfide cross-linkers for natural rubber/carbon black (NR/CB) composites. Two macrocyclic systems were designed to clarify the role of the interface integration. Tert-butylcalix[6]arene (TBC6), lacking polymerizable groups, forms polyrotaxane structures that operate primarily at the rubber-filler interface, enhancing bound rubber formation and enabling interfacial sliding. In contrast, allyl-functionalized calix[6]arene (ATBC6) covalently incorporates into the vulcanized network, constructing slidable cross-links within the bulk while simultaneously strengthening rubber-filler interfacial coupling. This coordinated network interface architecture promotes efficient stress transfer and suppresses crack propagation. The ATBC6-based composite exhibits a 140% increase in tear strength and a 340% enhancement in fracture toughness relative to those of conventional vulcanizates, accompanied by pronounced strain-rate hardening and improved energy absorption. Additionally, stable polysulfide linkages and phenolic units impart enhanced thermo-oxidative aging resistance. This scalable interface engineering strategy offers a practical pathway toward high-performance elastomer composites.