Un-ionized polyurethane was obtained by the reaction of an isocyanate-terminated urethane prepolymer, which was synthesized from 4,4'-diphenylmethane diisocyanate and poly(oxytetramethylene)-alpha,omega-glycol, with 2,2-bis(hydroxymethyl)propionic acid. A carboxylate-based polyurethane anionomer was then derived from the polyurethane by the use of the sodium, potassium, or magnesium salt of acetic acid as a neutralizer. The ionomerization resulted in the following changes in the characteristics of the polyurethane: (1) an increase in the tensile strength, (2) a decrease in the glass-transition temperature, (3) an increase in the wettability and hygroscopicity with respect to water, and (4) susceptibility to thermal decomposition. A sulfonate-based polyurethane was also synthesized for comparison with the carboxylate-based polyurethane. (c) 2005 Wiley Periodicals, Inc.