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 anionomer (UAA) precursor chains. The microstructures of these networks are very sensitive to the nature of and the amount of solvent used during crosslinking. Whereas dioxane forms relatively homogenous solution, water preferentially interacts with hydrophile segment of UAA chains, causing the microphase separation between hydrophilic moieties and hydrophobic main chains. This 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 quite 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 confirmed by measuring the contact angle to water. These microphase-separated hydrophilic domains on UAA gel matrix, which are observed by scanning electron microscopy measurement, influence the mechanical property of dried UAA gels as well. (C) 2000 John Wiley & Sons, Inc.