Synthesis and characterization of pH-sensitive microgels by derivatization of npa-based reactive copolymers

There has been an increased interest in recent years in evaluating the swelling behaviour of pH-sensitive polymer gels, since they are potentially useful in a wide range of applications such as biomedical materials, biosensors, and the removal of contaminants from sewage waste. Nanosized NPA-based copolymers have been synthesized and chemically modified in order to introduce ionizable pendant groups with different pKa into the macromolecular networks. These modification reactions were controlled by 1H NMR and UV spectroscopy. SEM micrographs of modified microgels show samples to be monodisperse spheres. The pH-sensitivity of the final microgels has been studied by the determination of the hydrodynamic diameters by QELS as a function of pH. All the systems underwent a swelling transition near the estimated apparent pKa according to the introduced pendant groups. The pH-sensitive equilibrium swelling behaviour of microgels derivatized with 4-methylpyridyne has been studied as a function of ionic strength and copolymer composition. There are some facts related to the ionizable pendant groups that influence and determine the pH-responsive swelling behaviour of microgels, such as the pKa, content, accesibility of these groups, and ionic strength of external solution. According to this, a simple and versatile derivatization strategy has been employed to design intelligent microgels with specific pH-sensitive swelling properties.