AbstractAqueous polyurethane dispersions derived from various polycarbonatediols, m‐di(2‐isocyanatopropyl)benzene(TMXDI), and various carboxylic diols including dimethylol propionic acid (DMPA), dimethylol butyric acid (DMBA), and a carboxylic polycaprolactonediol (Placcel 205BA) were prepared by a method in which the dispersing procedure was modified to enhance the molecular weight. The NH2/NCO ratio during chain extension affected the molecular weight of the polyurethanes, significantly, and an optimum ratio of 0.67:1.0 was used. The molecular weight, particle size, tensile properties, and thermal properties of the polyurethane dispersions were investigated. The effect chemical structure of the polycarbonatediols on the properties shows no obvious trend, but the polyurethane dispersions derived from the carboxylic polycaprolactonediol exhibit smaller particle size and softer tensile properties when compared with those derived from DMPA and DMBA. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers