Enthalpy of the Complexation in Electrolyte Solutions of Polycations and Polyzwitterions of Different Structures and Topologies

Our understanding of the intricate complexation behavior of polyzwitterions with polycations is less than that of polyanion-polycation complexes. In addition, the effect of the topology of polyzwitterions on the complexation of polyzwitterions with polycations is also unclear. We investigated the complexation of methacrylate-based linear, star, and branched poly(sulfobetaine methacrylate)s (PB) with the cationic poly(methacryl oxyethyl trimethylammonium chloride) (PMOTAC), as well as the complexation of linear imidazolium-based polyzwitterions and polycations, by isothermal titration calorimetry (ITC) in saline media. The complexation enthalpies increased with increasing salt concentration and molecular weight up to 0.25 M NaCl. A low degree of branching had little effect on the complexation, whereas highly branched PB did not form complexes. The obtained complexes had nonstoichiometric composition, with high enthalpies per mole of injected polycation due to additional water being released by cascading complexation. Understanding the complexation behavior of polyzwitterions with polycations provides alternatives to traditional polyanion-polycation complexes.