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. The morphology and physical properties of polyisoprene ionomers co-neutralized with Na+ and Mg2+ in different ratios have been studied. The mechanical and self-healing properties of the ionomer were reinforced and disturbed, respectively, at over 25 % of the Mg2+ ratio, where linkage via Mg2+ in the network is pervasive throughout the material.