Effect of the Mg²⁺ ratio on the mechanical and self-healing properties of polyisoprene ionomers co-neutralized with Na⁺ and Mg²⁺

The effect of the ratio of divalent (Mg²⁺) to monovalent (Na⁺) cations on the mechanical and self-healing properties of polyisoprene (PI) ionomers co-neutralized with Na⁺ and Mg²⁺ was studied. Sodium carboxylates link polymer chains via electrostatic interactions, while magnesium carboxylates more strongly link polymer chains via ionic bonds. Therefore, Mg²⁺ considerably reinforces the PI ionomer. However, we found that the mechanical properties of the PI ionomers did not change proportionally to the ratio of Mg²⁺. The ionomer was significantly reinforced at over 25% of the Mg²⁺ ratio, where linkage via Mg²⁺ in the network was prevalent throughout the material. At the same time, the self-healing of the PI ionomer was disrupted.