Order maintains within an alkaline-earth metal carboxylate ionic nanocluster covalently constrained by poly(methyl methacrylate) chain segments

Whether alkaline-earth metal carboxylate ionic nanoclusters can retain internal order when covalently constrained by polymer chains remains unclear. Here, a methyl methacrylate–methacrylic acid copolymer (MMA–MAA) was neutralized with acetate salts of Mg 2+ , Ca 2+ , Sr 2+ , and Ba 2+ to form a series of metal–carboxylate ionomers. FT-IR and ICP-OES verify metal–carboxylate formation with comparable degrees of neutralization, while TGA shows a delayed onset of mass loss and a small high-temperature residue. High-resolution TEM reveals distinct lattice fringes inside ionic domains, indicating preserved short-range order under covalent confinement. Consistently, WAXS combined with an operational difference-subtraction analysis yields a broad cluster-related feature centered at 2 θ  ≈ 21.8°, supporting ensemble-level intra-cluster correlations. DSC further shows a weak low-temperature endotherm that intensifies upon vacuum aging, suggesting progressive structural development within ionic domains. Together, these results provide cross-technique evidence for preserved and aging-enhanced short-range order in alkaline-earth metal carboxylate nanoclusters and clarify how ionic associations evolve under covalent constraints. Graphical abstract MMA–MAA salt ionomers with –COO⁻M²⁺ ionic clusters are systematically studied. HR-TEM images reveal lattice fringes inside the clusters, giving direct proof of internal ordering. DSC results show aging-induced low-temperature endothermic peaks, confirming that nanoscale ordering develops progressively. These findings demonstrate that ionic domains can retain internal order even under covalent constraints from polymer chains.