Microstructure-viscoelasticity relationships in melt state ionomers and blends

High-density Coulomb interactions in polyelectrolyte complexes (PECs) enhance mechanical properties but make processing challenging due to limited chain mobility. In contrast, ionomers exhibit thermally activated chain relaxation by dissociating ionic crosslinks at elevated temperatures. Our work aims to combine the thermoplastic behavior of ionomers with the thermosetting characteristics of PECs. By investigating ionomers and their binary blends with oppositely charged counterparts, we established microstructure-viscoelasticity relationships to gain insights into materials design for higher reprocessability and sustainability.

Both ionomers and blends exhibit viscoelastic liquid behavior with superb reprocessability. By controlling charge density, identity, and distribution, the linear viscoelasticity is tunable over a wide frequency range. Ionomer dynamics are tightly associated with their microstructures, as measured by SAXS/WAXS. High charge density anionic ionomers form distinct ionic clusters with spacings of 3.4-3.8 nm, which significantly delay terminal relaxation and contribute to higher viscosity. In the blends, the partial dissociation of potassium sulfonate clusters results in lower viscosity compared to the parent anionic ionomer. Additionally, diblock ionomer self-assembles into well-ordered lamellae. This ionically stabilized microstructure contributes to an extended rubbery plateau, enhancing the material’s thermal and mechanical properties.