Anti-polyelectrolyte effect of zwitterions containing (meth)acrylic waterborne polymer chains as tool for colloidal stabilization and polymer reinforcement

The anti-polyelectrolyte effect, a characteristic unique to polymer chains containing zwitterions, was investigated for its impact on colloidal stabilization during emulsion polymerization and on the resulting polymer characteristics. The zwitterionic monomer (ZM) 3-[(3-Acrylamidopropyl)dimethylammonio]propane-1-sulfonate (A3361) was selected for the synthesis of 30 wt% emulsifier-free methyl methacrylate/n-butyl acrylate (MMA/n-BA) polymer latex. Three pH conditions were examined: neutral, where the zwitterionic chains are in a collapsed state, and acidic and basic, where these chains adopt an extended conformation, leading to the anti-polyelectrolyte effect. The study of the anti-polyelectrolyte phenomenon on colloidal stability was challenging due to the increased ionic strength in the dispersions. Nevertheless, films cast from the acidic latex demonstrated enhanced mechanical properties, water resistance, and humidity barrier compared to films produced at neutral pH. This improvement is attributed to the anti-polyelectrolyte phenomenon, where the extended polymer chains rich in zwitterions offer enhanced ionic complexation, resulting in a denser and thicker ionic complexed network within the MMA/n-BA matrix. Under basic pH conditions, these improvements were modest, indicating that the anti-polyelectrolyte mechanism is influenced by pH. Furthermore, the high incorporation of A3361 facilitated, for the first time, the synthesis of 50% solids content emulsifier-free latexes, highlighting practical importance of this technology.