Synthesis and characterization of solvent-free waterborne polyurethane dispersion with both sulfonic and carboxylic hydrophilic chain-extending agents for matt coating applications

Simultaneously using sulfonic and carboxylic acid as hydrophilic chain-extending agents, a new type of solvent-free and chemical matt waterborne polyurethane resin was prepared and investigated. The chemical structure containing urethane and urea groups in this novel carboxylate/sulfonate type of waterborne polyurethane (CSWPU) resin was confirmed by FTIR, 1H and 13C NMR spectra. An obvious advantage for the environment is that, unlike the traditional synthetic method for waterborne polyurethane, the reactive system doesn't need any organic solvent to reduce the viscosity of the prepolymer in the process of prepolymerization. In addition, the gloss extinction was generated by the drying process of the resin itself, without the requirement of any matting agents. 3D-AFM images indicate that the surface of the matt CSWPU films was extremely rough and was comprised of many spherical particles with diameters in the range of 0.8–3.0 μm arranged on the films' surface. The matt CSWPU resin tended to have a relatively higher molecular weight and lower swelling ratio. Moreover, an increase of sulfonic hydrophilic chain-extending agent content or the initial molecular weight of the soft segment facilitated the improvement of thermal stability.