The technical difficulties in preparing high solid content waterborne polyurethane (WPU) with low viscosity have been discussed in this article. The phase inversion principle of WPU prepolymers was expounded
and the influence of material characteristics and process conditions of prepolymer on phase inversion and phase inversion point were analyzed. From the perspective of hydration layer
the influence of the hydration layer thickness on the solid content of WPU was discussed. In addition
the influence of the size and space density of latex particles on high solid content WPU with low viscosity was discussed. Finally
the future research work of high solid content WPU with low viscosity was prospected.