Facile and High-Yield Synthesis of Monodisperse and Heat-Resistant Polymaleimide Microspheres by Self-Stabilized Precipitation Polymerization

In recent years, monodisperse functional polymer particles have attracted intensive attention due to their promising prospects in numerous application fields. Herein, monodisperse polymaleimide (PMI) microspheres with excellent thermal stability and a high glass transition temperature were facilely prepared by self-stabilized precipitation polymerization (2SP) of maleimide. The effects of the reaction medium, monomer and initiator concentrations, reaction temperature, and cross-linker dosage on the size and morphology of the as-prepared PMI microspheres were systematically investigated. By simply adjusting the monomer and initiator concentration and reaction temperature, monodisperse spherical PMI microspheres were successfully obtained in high yield (close to 100%) in ethyl acetate with tunable diameters of 0.24–1.08 μm. To elucidate the nucleation, stabilization, and growth mechanism, the size, surface morphology, and molecular weight of the as-prepared PMI microspheres were monitored over the polymerization process. As expected, the particle growth was mainly attributed to the continuous deposition of newly formed PMI chains onto the surface of the PMI nuclei, which is in good agreement with the traditional 2SP process. Furthermore, the intermolecular hydrogen-bonding interactions between imide and carbonyl groups might also exert an important influence on the stabilization and growth of the PMI particles, which were verified by the 2SP polymerization of MI in the presence of urea and succinimide.