Synthesis of Polyurethane Dispersions in Nanoparticles and Their Properties that Depend on Aging Time

Waterborne polyurethane dispersions in nanoparticles were synthesized from poly (propylene glycol), isophorone diisocyanate, and dimethylolpropionic acid in a modified prepolymer process. Three groups of specimens with variations in hard-to-soft segment molar ratios were synthesized in Group A experiments to confirm the recipe of waterborne polyurethane, whose particles have the smallest mean particle size and the narrowest particle size distribution. Group B experiments, which consist of five samples, were designed based on the results of Group A experiments. The variable of each sample was one kind of raw materials' content compared with the confirmed recipe in Group A experiments. Relationships among variations in viscosity, mean nanoparticle size, and nanoparticle size distribution over time were analyzed. It was found that the viscosity of all samples increased, mean nanoparticle size remained constant or decreased, and nanoparticle size distribution became narrow over time. Our work provides a new recipe for the preparation of waterborne polyurethane of nanoparticles with excellent stability. Moreover, aging time is considered to be a key index to viscosity, particle size, and particle size distribution in the polyurethane dispersion.