Complexation of homologous polyions with variable polarity

Polyelectrolyte complexation is sensitive to both long-ranged electrostatic interaction and short-ranged effects including solvation and ion association. We synthesized polyanions and polycations with identical backbone, variable length, and controlled solvation environment around charges. Systematic dependences on molecular weight and local environment are revealed by accurate polymer compositions determined using spectroscopic measurements, for nine sets of polymer pairs. Using two fitting parameters, the backbone solubility parameter and the ion-binding strength, the results are quantatively described by a solution free energy model that incorporates properly charge connectivity and ion-binding equilibrium.