Moving Beyond Oligoethers: Polar Side‐Chain Engineering for Aqueous Mixed Ionic–Electronic Conductors

Organic mixed ionic‐electronic conductors (OMIECs) often use oligoether (OE) side chains to enable aqueous redox activity, but non‐optimized OE chains can cause excessive swelling during electrochemical doping, disrupting polymer order and impairing electronic transport. Alternative polar functionalities —such as esters, alcohols, and carboxylates — can offer properties atypical of those achieved with OE side chains. Here, we investigate how different polar side chains and functional groups affect redox performance and mixed transport in 3,4‐propylenedioxythiophene polymers (PProDOTs) with OE (POE3‐co‐DMP), hydroxyl (POH), or carboxylic acid (PCOOH) substituents. We show that OE chains are not required for bulk doping in aqueous electrolytes: short, polar protic groups preserve or enhance redox activity. Replacing oligoether chains with hydroxyl or carboxylic acid groups lowers oxidation potentials by ∼200 mV and increases electrochemical conductivity by up to nearly 200%. POH exhibits faster doping kinetics, doubling the electrochemical response rate while reducing swelling. Hydrogen bonding in POH and PCOOH films also limits mechanical softening during redox cycling, maintaining film stiffness. These findings highlight short, polar side chains as a powerful strategy for fine‐tuning redox potential, ionic‐electronic transport, and mechanical robustness in OMIECs, expanding the design space for aqueous‐compatible conjugated polymers beyond oligoether‐functionalized systems.