Synthesis of polyurea–polyether nanoparticles via spontaneous nanoprecipitation†
We describe here a novel synthetic route for the preparation of polyurea–polyether nanoparticles (PNPs) that can be performed in a single solvent and which does not require the use of a preformed polymer. First a low molecular weight polyether-monoamine (poly(PO/EO)) is added drop wise to a solution of 4,4′-methylene-diphenylene isocyanate (4,4′-MDI). This leads to a solution of free 4,4′-MDI and low molecular weight 4,4′-MDI-functionalized poly(PO/EO). In a second stage a short diamine chain extender and additional 4,4′-MDI are added drop wise to the solution. This results in the formation of an ABA polyether–polyurea–polyether block copolymer that spontaneously precipitates forming nanoparticles (PNPs). The PNPs were characterized using a variety of techniques including transmission electron microscopy (TEM), photon correlation spectroscopy (PCS) and X-ray photoelectron spectroscopy (XPS). The combined analysis suggests that the polyether-monoamine resides preferentially on the surface of the PNPs and has a role in their stabilization as well as in the stabilization of the resulting colloidal suspensions. The nature of the diamine chain extender was varied in order to explore its effect on the formation, properties and morphology of the nanoparticles. PNPs in the size range from 20 to 100 nm were obtained depending on the diamine used and the stability of the colloidal solution obtained was also found to be dependent on the diamine used.