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 pK(a) into the macromolecular networks. These modification reactions were controlled by H-1 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 pK(a) 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 pK(a), 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. (C) 2008 Elsevier B.V. All rights reserved.