Counterion-Free Ionic Associating Polymers via In-Situ Ionization

The performance of oppositely charged polymer blends is often limited by the endogenous small molecule counterions that screen electrostatic interactions and weaken the polymer network. To address this, we introduce a robust strategy to synthesize counterion-free ionic associating polymers (IAPs) by reactively blending two charge-neutral telechelic poly (ethylene glycol) (PEG) oligomer precursors, A2 and B2, bearing imidazole and ethyl sulfonate end groups, respectively. Upon blending, B2 quaternizes A2 via the "ethyl group transfer" reaction, resulting in cationic A2 (2+) and anionic B2 (2-). Such in-situ ionization leads to a counterion-free IAP with a 2-fold increase in viscosity compared to the PEG precursors, confirming the formation of a transient dynamic network driven by unscreened ionic associations. Pulsed-field gradient NMR (PFG-NMR) was used to probe the molecular-level dynamics. Notably, the product of the diffusion coefficient and viscosity (Dη) for the IAP shows a significant positive deviation from the Rouse model prediction. This finding indicates a partial decoupling of microscopic chain mobility from macroscopic viscous flow. This is a characteristic of associating networks where local chain "hopping" occurs on a faster timescale than global network relaxation. The modular, counterion-free platform enables the design of dynamic polymers with precisely tunable properties, opening new avenues for creating recyclable and sustainable materials.