Phase Transition Behavior of HPMC-AA and Preparation of HPMC-PAA Nanogels

Abstract

The lower critical solution temperature (LCST) of hydroxypropyl methylcellulose (HPMC) under mixing with acrylic acid (AA) monomer has been studied by turbidity measurements. It has been found that the LCST of the HPMC was drastically reduced from 60°C to 38°C with the increase of the concentration of AA, while the HPMC is kept at 0.5 wt%. The driving force shifting the LCST is attributed to the hydrogen bonding and hydrophobic interaction of the molecules. Then surfactant-free HPMC-PAA nanogels have been synthesized via the polymerization of AA monomer with the collapsed HPMC as a template or core at their LCST, using KPS and TEMED as redox initiator in the presence of BIS as cross-linking agent. HPMC-PAA nanogels have 50~150  nm diameters characterized by transmission electron microscope and dynamic light scattering. The HPMC-PAA nanogels exhibit the temperature phase transition behaviors, and these nanogels' volume phase transition temperature is close to the LCST of HPMC/AA system.