In Situ Constructed Covalent‐Ionic Dual Network in <scp>HNBR</scp> for Synergistic Mechanical Reinforcement and Thermal Stabilization

ABSTRACT Hydrogenated nitrile butadiene rubber (HNBR) is widely used in various demanding fields due to its excellent oil resistance and mechanical properties. However, maintaining its superior mechanical performance and good elasticity under high‐temperature conditions remains a significant challenge. This study systematically investigates the effect of the zinc dimethacrylate (ZDMA)/carbon black (CB) ratio on the properties of HNBR‐based composites, including filler dispersion, mechanical performance, micromorphology, aging resistance, and cross‐link network structure. The results indicate that the combined use of ZDMA and CB improves filler dispersion and strengthens the filler‐rubber network within the vulcanizate. This network, comprising covalent cross‐links and a dynamic ionic network from ZDMA, provides exceptional synergistic reinforcement. Furthermore, replacing dicumyl peroxide (DCP) with 1,3‐Bis(tert‐butylperoxyisopropyl)benzene (BIBP) as the vulcanizing agent eliminates plasticizing by‐products, yielding a more stable covalent network. The synergy between this stable network and the dynamic ionic network markedly enhances both thermal stability and compression set resistance. An optimal overall performance is achieved at a ZDMA/CB ratio of 40/20, with the composite retaining a high tensile strength of 33.9 MPa even after aging.