Synthesis of high solid content waterborne polyurethanes with controllable bimodal particle size distribution

A series of waterborne polyurethane dispersions were synthesized by one-pot reaction and step-wise reaction, respectively. The effects of synthetic methods and DMPA content on the particle size distribution (PSD), solid contents and viscosity were studied by laser particle size analyzer, Brookfield viscometer and TEM analysis. High solid content and low viscosity waterborne polyurethanes (WPUs) with controllable bimodal PSD were prepared by one-pot reaction using 2,2-dimethylol propionic acid (DMPA) as the only self-emulsifier. Meanwhile, 40% solid content WPUs with unimodal PSD were obtained by step-wise reaction at the same formula. With the increment of DMPA content, the ratio of large particles to small particles decreased and two peaks of the particle size finally became one peak by one-pot reaction while the PSD remained unimodal by step-wise reaction. The reason leading to the difference of PSD between one-pot reaction and step-wise reaction was analyzed and the relationships among PSD, viscosity and solid content were discussed. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131 , 40420.