Structure–Property Relationships and Thermal Aging of EPDN/NBR Elastomer Networks Modified With Polydiene and Maleimide Additives

This study investigates the structure–property relationships in binary elastomer systems based on ethylene–propylene diene copolymer (EPDN) and nitrile–butadiene rubber (NBR) modified with polydiene (PD) and dithiobis-maleimide (DTBFM) functional additives. The combined influence of reactive unsaturated rubber, polydiene modifiers and maleimide crosslinkers on crosslink density, gel fraction, rheological behavior, mechanical properties and thermal-oxidative stability was systematically analyzed for EPDN/NBR blends with component ratios of 80:20, 70:30 and 60:40. The results demonstrate that increasing NBR content significantly enhances radical-induced crosslinking due to the presence of carbon–carbon double bonds and polar nitrile groups, leading to the formation of a more developed spatial network. The introduction of polydiene and maleimide additives promotes the formation of hybrid elastomer networks, which is reflected in the increase of gel fraction, Mooney viscosity and crosslink density calculated using the Flory–Rehner approach. A clear correlation between network architecture and mechanical performance is established. An optimal balance between processability, mechanical strength and thermal-oxidative resistance is achieved at an EPDN/NBR ratio of 60:40, which exhibits the highest tensile strength, hardness and durability under thermal aging conditions. The obtained results indicate that targeted reactive modification using a combination of NBR, polydiene and maleimide additives represents an effective strategy for tailoring the network structure of EPDN-based elastomers. This approach enables the development of durable elastomer materials with controlled properties for demanding industrial and engineering applications without the use of conventional sulfur curing systems.