Preparation and characterization of uniform polyurea microspheres via an environmental-friendly synthetic process: The swelling and shrinkage phenomena

Abstract

In this work, a non-toxic isocyanate HDB-LV is used for the first time to produce monodispersed polyurea microspheres with a size from 10 to 40μm via a microfluidic droplet approach. The toxic ethylenediamine which is usually necessary for the synthesis of polyurea, is found to be not adaptable for the formation of polyurea microspheres because it can either cause swelling (at low amine concentration) or deformation (at high amine concentration) of the microspheres. A theoretical mechanism for the swelling phenomenon of microspheres is elucidated. Alternatively, thermal hydrolysis of isocyanates that can generate amines is proven to be very effective for the synthesis of polyurea microspheres. A linear relationship between the sizes of microfluidic droplets and polyurea microspheres is found and discussed quantitatively. In the end, the polyurea microspheres from 2 to 40μm are characterized to have no obvious scattering effects against UV.