Synthesis of novel amphiphilic pH-sensitive polyurethane networks through water-in-oil soap-free emulsion polymerization process. I. Microstructural differences and swelling behaviors

pH-sensitive amphiphilic networks are synthesized from urethane acrylate an ionomer (UAA) precursor chains. The microstructures of these networks are v ery sensitive to the nature of and the amount of solvent used during crossl inking. Whereas dioxane forms relatively homogenous solution, water prefere ntially interacts with hydrophile segment of UAA chains, causing the microp hase separation between hydrophilic moieties and hydrophobic main chains. T his microphase separation was locked-in by crosslinking reaction, enhancing largely the hydrophilicity of UAA networks and the hydrophobic aggregation . The UAA gels, prepared with water (UAAG) and/or dioxane (UADG), exhibit q uite different swelling behaviors in the same dissolution medium because of their completely different microstructures. The improved hydrophilicity of UAAG gels due to the hydrophilic/hydrophobic microphase separation is conf irmed by measuring the contact angle to water. These microphase-separated h ydrophilic domains on UAA gel matrix, which are observed by scanning electr on microscopy measurement, influence the mechanical property of dried UAA g els as well. (C) 2000 John Wiley & Sons, Inc.