Polyzwitterions

Polyzwitterions are polymers in which repeating units contain both positive and negative charges in close proximity, typically as internal zwitterionic groups on side chains or in the main chain. These groups are often inner-salt betaine motifs, such as a quaternary ammonium center paired with a sulfonate or carboxylate group.

Polyzwitterions are overall electrically neutral, in contrast to polyelectrolytes that carry a net charge. The local charge separation creates strong hydration and minimizes nonspecific protein adsorption, yielding inherently nonfouling, biocompatible materials. The chains can swell or collapse depending on ionic strength and the balance of attractive and repulsive interactions.

Common zwitterionic monomers include sulfobetaine methacrylate (SBMA), carboxybetaine methacrylate (CBMA), and related acrylamides. Polyzwitterions are synthesized by radical polymerization, including conventional, atom transfer radical (ATRP), or reversible addition–fragmentation chain transfer (RAFT) methods, enabling random, block, and branched architectures with side-chain zwitterions.

Applications include antifouling coatings for medical devices and marine environments, nonfouling surfaces, hydrogel matrices for tissue engineering and controlled release, and lubricious coatings for implants. Some polyzwitterions show anti-polyelectrolyte effects, swelling with added salt due to screening of intramolecular charges, and high hydration across a broad pH range.