Production of polyurea microspheres with a non-toxic chemical system.

• Controllable and uniform size of solid polyurea microspheres from 2 to 40 μm.

• Swelling mechanism investigation of polyurea microspheres for low amine concentrations (<0.025 wt%).

• A universal relationship between the size of isocyanate droplets and final polyurea microspheres.

• Investigation of UV scattering effects of polyurea microspheres.