"Inverse polyampholyte" hydrogels from double-cationic hydrogels: Synthesis by RAFT polymerization and characterization

Abstract

We present two novel, homologous, pyridine-based monomers, 2-(pyridin-2-yl)ethyl methacrylate (PyEMA) and (pyridin-2-yl)methyl methacrylate (PyMMA), which, despite their structural similarity, the former can be readily thermolyzed to methacrylic acid, while the latter remains intact under the same conditions. This was most dramatically demonstrated in the present work, where PyEMA and PyMMA were randomly terpolymerized with a dimethacrylate cross-linker using reversible addition-fragmentation chain transfer polymerization to yield weakly double-cationic polyelectrolyte hydrogels of three different compositions which, upon thermal treatment, they were readily converted to polyampholyte hydrogels. While the parent double-cationic polyelectrolyte hydrogels exhibited a swelling response only to low-pH conditions, the daughter polyampholyte hydrogels presented swelling responses to both high- and low-pH conditions. Owing to the relative values of the effective pKa's of the weakly acidic and weakly basic units, with the latter being lower than the former ("inverse polyampholyte" behavior), the swelling profiles of the daughter hydrogels were insensitive to polyampholyte composition. © 2014 American Chemical Society.