Terminal Crosslinking Programs Dynamic Entanglement Networks in Fatigue-Resistant Polyisoprene Elastomers

Abstract

The fatigue resistance of elastomers is fundamentally governed by molecular entanglements, yet existing approaches depend on preserving entanglements inherited from polymer synthesis—imposing strict constraints on molecular weight and processing while yielding static network topologies. Here we report terminal crosslinking and entanglement networks (TCENs), a strategy that programs topological constraint networks. Reactive methacrylate or olefinic groups installed exclusively at polyisoprene chain termini undergo preferential crosslinking, generating locally concentrated crosslink architectures interlaced with exchangeable polysulfide linkages. Double-quantum NMR confirms up to 16% higher entanglement density and 31% fewer network defects relative to conventionally crosslinked polyisoprene. The optimized elastomer achieves a fatigue threshold of 1458 J m^–2 (tenfold enhancement), elevenfold improved fracture toughness, and retains over 97.8% of its dynamic stiffness after 5 × 10⁵ loading cycles, while maintaining low hysteresis, it even outperformed natural rubber (NR). Molecular dynamics simulations reveal that dynamic sulfur bond exchange coupled with strain-responsive crosslink-enriched regions enables adaptive stress redistribution. This topology-programming concept provides a scalable route to high-performance elastomers fully compatible with industrial vulcanization.