Double‐Network Structure Significantly Improves Both Strength and Toughness of Nitrile‐Butadiene Rubber by Introducing Poly (Acrylonitrile‐<i>Co</i>‐Butyl Acrylate) Elastomer

ABSTRACT In order to obtain nitrile‐butadiene rubber (NBR) with both high strength and high toughness, composites with a double network were prepared by introducing poly (acrylonitrile‐ co ‐butyl acrylate) elastomer. The P(AN‐ co ‐BA) elastomer was randomly copolymerized by acrylonitrile (AN) and butyl acrylate (BA). The second network was formed by the crystal crosslinking of the P(AN‐ co ‐BA) elastomer. The tensile strength and toughness of the composites were 460% and 305% of NBR, respectively. The curves of differential scanning calorimetry (DSC) exhibited peaks representing melting in the heating curves of both P(AN‐ co ‐BA) and P(AN‐ co ‐BA)/NBR composite, demonstrating crystallization in both elastomers and composites. The results of low‐field nuclear magnetic resonance (LF‐NMR) showed that the crosslink density of the composite is greater than the linear sum of the crosslink density of the NBR and the crosslink density of the elastomer, informing that the physical cross‐linked networks remain in the composite after sulfurization and new physical crosslinking appears between the NBR molecular chain and the P(AN‐ co ‐BA) molecular chain. The results of scanning electron microscopy (SEM) showed that the composite exhibits a uniform distribution with interpenetrating phases. This study provides a new approach for preparing NBR composites with both high strength and high toughness.