Understanding anti‐polyelectrolyte behavior of a well‐defined polyzwitterion at the single‐chain level

A study was made of the anti‐polyelectrolyte effect of a model polyzwitterion at the single‐chain level and from the point of view of comparison with inorganic salts and organic inner salts. A well‐defined polymer of sulfobetaine was synthesized and fluorescently labeled. Fluorescence correlation spectroscopy was adopted to probe diffusion and chain size of polyzwitterion single chains in extremely dilute aqueous solutions over a broad concentration range of added salts. By the introduction of inorganic salts and organic inner salts, the single chains of polyzwitterions expanded with an increase of salt concentration. This observation indicates that the break‐up of the dipole–dipole attraction between the zwitterion units is the mechanism of the anti‐polyelectrolyte effect of polyzwitterions. The difference in the strength of the anti‐polyelectrolyte effect induced by inorganic salts and organic inner salts also indicates the partial contribution from the asymmetric adsorption of ions onto polyzwitterion chains.