Structures, properties, and applications of zwitterionic polymers

Zwitterionic polymers have attracted research attention in recent years owing to their unique molecular structures. In the same repeat unit, positive and negative charges are simultaneously located on a pair of cationic and anionic groups; therefore, zwitterionic polymers have a large dipole moment and numerous charged groups. Although the molecular chain of the zwitterionic polymer can be maintained in an electrically neutral state overall, the coexistence of the oppositely charged groups confers extremely high polarity and excellent hydrophilicity to the polymer. At the same time, the electricality of the polymer can be further regulated by the environmental pH and salt ions, which greatly broadens the scope of applications in different fields. This review introduces various structures of zwitterionic polymers and analyzes the reasons why zwitterionic polymers exhibit pH responsiveness, anti-polyelectrolyte effects, and superior electrical conductivity. The application fields are also summarized by generalizing the research status of zwitterionic polymers, including applications in antifouling coatings, drug delivery, wastewater treatment, and sensors, etc.