Preparation of core–shell and hollow polyurea microspheres via precipitation polymerization using polyamine as crosslinker monomer

A novel type of hollow polymer particles, polyurea (PU) microspheres with uniform morphology, is prepared via precipitation polymerization of isophorone diisocyanate (IPDI) in acetone–H2O as the solvent in three steps. In the first step, IPDI reacts with H2O to form the core particles consisting of linear PU, followed, in the second step, by addition of triethylene tetramine (TETA) and supplementary IPDI; the microspheres of core–shell structure are therefore obtained with a shell consisting of crosslinked PU thanks to the copolymerization of TETA with IPDI. Hollow microspheres are finally obtained by dissolving the core template of linear PU. The influence of the amounts of TETA, IPDI and their molar ratio on the formation and the morphology of the core–shell and the hollow microspheres are studied. The morphologies of the core–shell and of the hollow microspheres are characterized by scanning electron microscopy. The polymers are examined using Fourier-transform infrared spectra, differential scanning calorimetry and thermogravimetric analysis.