Hydrophilic Polyethers Derived from Functional Epoxides: Beyond Poly(ethylene glycol)

Hydrophilic polymers constitute an essential section in polymer sciences and technologies. Poly(ethylene glycol) (PEG), a flagship hydrophilic polymer derived from the simplest epoxide, has attracted massive research interests and found wide-ranged applications from daily commodities to cutting-edge materials. In the meantime, limitations of PEG are increasingly noted, including hazardous nature of its monomer, unfavored crystallinity, lack of modification sites and stimuli-responsiveness, immunogenicity due to extensive uses, etc., which has heavily spurred explorations for PEG alternatives. This review summarizes the synthetic methods, properties, and applications of non-PEG hydrophilic polyethers containing methoxyl, hydroxyl, carboxyl, amido, amino, and other polar pendant groups derived from functional epoxide monomers. To a large extent, these polymers maintain the key characters of PEG (e.g. water solubility, biocompatibility), and feature tunable stimuli-responsiveness (to temperature, pH, oxidation), chemical modifiability, and even degradability. The current challenges and opportunities for future advancement of non-PEG hydrophilic polyethers are also proposed.