Designing Hydrogel Microspheres from Liquid-Liquid Phase Transitions of Aqueous Polymer Solutions

Abstract

<p>This thesis focuses on reactive water-soluble polymers suitable for forming liquid-liquid phase transitions from both polyelectrolyte complexation and thermal induction. Novel hydrogel microspheres are formed by liquid-liquid phase transition followed by crosslinking reactions. Besides studying the properties of polymers and hydrogel microspheres formed, the mechanism of liquid-liquid phase transitions as well as potential applications of these systems in protein separation and encapsulation are discussed. Chapter 1 describes the background of liquid-liquid phase transitions of aqueous polymer solutions, including polyelectrolyte complexation, thermally nduced phase transition and their application in designing hydrogel microspheres. Chapter 2 describes the thermo-responsive properties of fully MPEG-grafted maleic anhydride copolymers in aqueous solutions. The phase transitions are ascribed to the cooperative effects of intra/intermolecular hydrogen bonding and hydrophobic interactions. Chapter 3 describes the use of analogous partially MPEG-grafted maleic anhydride copolymers as reactive polyanions to form phase-separated liquid polyelectrolyte complexes with polycations, and to prepare hydrogel micro spheres by crosslinking the polyelectrolyte complexes with polyamines. Chapter 4 and Chapter 5 extend this two-stage approach of liquid-liquid phase transition followed by crosslinking reaction to thermally induced phase transitions. Thermally induced liquid-liquid phase transitions of poly(N,N-dimethacrylamide-coglycidyl methacrylate) and poly(N,N-dimethylacrylamide-co-allyl methacrylate) aqueous solutions are thus used to prepare hydrogel microspheres. The morphology of the resulting micro spheres is studied by electron microscopy. The mechanism of thermally induced liquid-liquid phase transitions ofpoly(N,Ndimethacrylamide) copolymer solutions is discussed in Chapter 6, together with the preparation of well-defined model copolymers using atom transfer radical polymerization.</p>