The addition of monovalent salts to polyelectrolyte complexes (PECs) comprising oppositely charged polyelectrolytes results in diminishing propensity for complexation, leading to complexes with higher water contents and lower moduli. However, the corresponding influence of multivalent ions on polyelectrolyte complexation has not yet been explored beyond enhanced screening effects. Here, we elucidate the significant impact of the valency of the salt cation on the composition, ion partitioning, and viscoelasticity of charge‐matched PECs comprising sodium salt of poly(acrylic acid) and poly(allylamine hydrochloride). Notably, preferential partitioning of divalent cations (Ca2+ and Sr2+) into the complexes is observed, in stark contrast to the depletion of monovalent ions (Na+) from the complexes. Concomitantly, electrostatic bridging of polyanion chains by divalent ions is found to hinder their relaxation, manifesting as a non‐monotonic evolution of the shear moduli of the complexes with increasing divalent salt concentrations. Relatedly, a failure of time‐salt and time‐ionic strength superposition approaches in presence of divalent ions is demonstrated, highlighting the nontrivial influence of these ions on chain relaxation behavior.

We present a simple approach to upcycle glycolyzed polyurethane foam products by fabricating robust, highly filled organic/inorganic composites (46–60 wt % solid loading). These composites, consisting of recycled polyols, naturally occurring or synthetic aluminosilicate minerals, and isocyanate linkers, are shown to possess superior mechanical (flexural) properties compared to ordinary Portland cement (OPC). Optimization of chemical composition (isocyanate and inorganic content) and curing temperatures (25–50 °C) results in low-density composites (up to 3× less dense than OPC) with flexural strengths comparable to OPC while exhibiting strain capacities up to 5× as compared to OPC-based systems. In contrast, parallel fabrication approaches using low OH-value virgin polyols resulted in flexible composites and much lower flexural strengths, highlighting the advantage of employing high −OH density recycled polyols. Variations in the flexural strength of the composites were correlated with differences in their morphologyuniformity in the distribution of inorganic particles contributed to improved flexural properties. The generality of this fabrication approach is demonstrated using quartz sand as the inorganic particle and recycled polyols with different hydroxyl values.

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