Poly(ethylene glycol) Becomes a Supra-Polyelectrolyte by Capturing Hydronium Ions in Water
Nanpu Cao, Yuehua Zhao, Hongbo Chen, Jinying Huang, Miao Yu, Yu Bao, Dapeng Wang, Shuxun Cui
Abstract
Poly(ethylene glycol) (PEG) has been widely used for decades as a “gold standard” in bioconjugation, nanomedicine, and antifouling. Although being extensively studied since 1859, PEG remains mysterious, as can be exemplified by the facts that PEG is the only polyether showing excellent water solubility, and the molecular structure of PEG is surprisingly simple if the fantastic properties are considered. Since PEG is usually used in an aqueous medium, the interactions between PEG and water should be the key to understanding the mechanism. Here, we find that by capturing hydronium ions (H3O+) in water, PEG changes from a neutral polymer to a supra-polyelectrolyte, which is a new category of polymer that becomes a polyelectrolyte when an external ion is dynamically bonded to the polymer via intermolecular interactions. This conclusion is supported by multiple experimental methods from the ensemble to single-molecule level. This finding casts new light on the relationship between the simple structure and fantastic functions of PEG. With known species of polymers and ions, numerous novel supra-polyelectrolytes can be prepared, which may present exciting properties in water.