Conjugated polyelectrolytes have been utilized in applications including chemical/biosensing, [30][31][32] cell imaging, [33][34][35] and disease diagnosis/therapy. [36,37] Their synthesis comprises the preparation of organic-soluble conjugated polymers followed by post-functionalization. A typical post-functionalization reaction is the nucleophilic substitution of an alkyl-bromide with amines to afford ammonium salts, which render the resultant conjugated polyelectrolytes aqueous soluble. However, post-functionalization exhibits poor conversion with many unreacted reaction sites. Aqueous polymerization of water-soluble monomers is an alternate approach realized through Heck, [38,39] Sonogashira, [40,41] Suzuki, [42,43] and FeCl 3 -mediated oxidative [44,45] polymerizations. These reactions are successful when the active species tolerates the presence of water.Reports of aqueous palladium-catalyzed DArP are scarce. [9,46,47] DArP also requires a carbonate base and carboxylic acid additive. Compared to water, carbonate bases display higher Lewis basicities, while carboxylic acids are more acidic. Palladium species preserve the reactivity in the presence of carbonates and carboxylic acids, making them tolerant to water. This study examines the aqueous palladium-catalyzed DArP of 2-bromothiophene derivatives, T1 and T2. The initially selected ligand, triphenylphosphine-3,3′,3″-trisulfonic acid trisodium salt (m-TPPTs), was functional in the DArP; however, its separation from the resultant polymers by dialysis was challenging due to its strong aggregation in water and N,N-dimethylacetamide (DMAc). This was supported by dynamic light scattering (DLS), X-ray crystallography, and gel permeation chromatography (GPC). Thus, pyrimidine-Pd(OAc) 2 was employed in the DArP of T1 to afford PT1 with no ligand (pyrimidine) contamination. Density functional theory (DFT) binding energy calculations revealed that the coordinating ability to palladium was of the order carboxylate > pivalic acid (PivOH) > water, rationalizing the feasibility of executing DArP in water. Finally, the polyelectrolyte molecular-weight overestimation by GPC in water was attributed to the polyelectrolyte effect. Experimental results indicated that the conjugated polyelectrolytes aggregate in DMAc to form a folding structure with the polar groups pointing outwards and conjugated moieties directed inwards, corresponding to a reduced hydrodynamic volume. The polyelectrolyte molecular weight and dispersity (Đ) values determined by GPC in DMAc were, therefore, questionable.