Monovalent salt induced simple coacervation of guanidinium-functionalized polyelectrolytes

Liquid-liquid phase separation (LLPS) is frequently induced by the non-covalent intermolecular associations such as electrostatic, π-π, cation-π, and hydrophobic interactions, which is actively observed in biological system. Recently, an arginine residue containing a flat and positively charged guanidinium functional group is of great interest due to the distinct amphiphilicity and strong interaction. Herein, the salt-induced LLPS of guanidinium-functionalized polyelectrolytes is addressed. The polyether-based guanidinium functionalized poly(allyl glycidyl ether) (G-PAGE) was synthesized by anionic ring-opening polymerization and post-modification. We observed that the G-PAGE solution shows that LLPS occurs when the electrostatic repulsion is sufficiently reduced by adding monovalent salt, and the coacervates follows the upper critical solution temperature (UCST) behavior. The larger and more polarizable monovalent anions screen the electrostatic repulsion more efficiently by counterion adsorption. Our finding suggests that that the π-π stacking between guanidinium groups is strong and crucial to lead the LLPS of guanidinium-rich polyelectrolyte in biological contexts.