ABSTRACT Ionomers are known to heal through thermally reversible ionic associations, though their healing efficiency is typically limited by a trade‐off with mechanical strength. In the present work, we report ∼88.4% self‐healing efficiency in ionically cross‐linked carboxylated nitrile rubber (XNBR) with an initial tensile strength of 21.0 MPa. In contrast, XNBR cross‐linked via mixed covalent and ionic modes showed 59% healing efficiency at 16.8 MPa strength. Healing was achieved via ex situ ammonia vapor exposure followed by thermal activation. In both cases, the characteristic stress upturn feature of the networks could be restored upon completion of the healing protocol. The inclusion of ammonia exposure prior to thermal healing significantly enhances self‐healing, surpassing the efficiencies reported for XNBR in earlier studies. Small‐angle X‐ray scattering (SAXS), Fourier transform infrared spectroscopy (FTIR) in reflection mode, and dynamic mechanical analysis (DMA) revealed that ammonia modulated the ionic associations and phase morphology of the networks. This modulation enhanced network mobility, thereby enabling efficient self‐healing. The reversible reorganization of these modified ionic domains is proposed as the underlying mechanism, offering a promising strategy for designing high‐strength self‐healing elastomers.
Billa et al. (Sat,) studied this question.