Synthesis of novel amphiphilic pH-sensitive polyurethane networks through W/O soap-free emulsion polymerization process. II. Mechanical property and biphasic swelling behaviors

Amphiphilic urethane acrylate anionomer (UAA) chains exhibited very differe nt solution properties in various solvents, such as water, dioxane, and dim ethyl sulfoxide (DMSO). UAA chains showed a polyelectrolyte effect in a hig hly polar solvent, DMSO, but gave constant viscosity at various concentrati ons in aqueous solution, because of the microstructural difference of the U AA chain formed in solvents. In polar solvents (water and DMSO), the swelli ng of UAA networks prepared with water and dioxane strongly depended on the properties of the hydrophilic domains. In low and nonpolar solvents (dioxa ne and methylene chloride), the swelling of UAA networks was only dependent on the property of the hydrophobic segments. In the polar solvent medium, UAAG networks prepared with water exhibited greater swelling than UADG netw orks prepared with dioxane. Concerning swelling in a nonpolar solvent, howe ver, UADG networks showed greater swelling than UAAG networks. This is beca use of the microstructural difference between these networks, which was con firmed by the mechanical, property measurement. UAAG networks, having highl y microphase-separated structures, had higher modulus and transition temper atures than the UADG networks, because of the microstructural difference be tween UADG and UAAG networks. Both the UAAG and UADG networks take up two i mmiscible solvents simultaneously within their hydrophobic and hydrophilic domains. Equilibrium swelling ratio of these networks in two immiscible sol vents strongly depends on their hydrophilic/hydrophobic balance that is con trolled by the type of solvent used in the network synthesis. (C) 2000 John Wiley & Sons, Inc.