Synthesis Of Polyacrylonitrile Microspheres With Anomalous Morphology By Stabilizer-free Dispersion Polymerization

Monodisperse peony-like polyacrylonitrile microspheres were prepared by a one-step approach in the presence of azodiisobutyronitrile as initiator without adding any stabilizer and mechanic stirring under reflux condition. Surface and structure characterizations of the particles were performed by methods such as transmission electron microscopy, scanning electron microscopy, X-ray diffraction, laser scattering particle size distribution analyzer and infrared spectrum. The results showed that the pure PAN microspheres are constructed by a number of nanoflakes, which thickness is around 10 nm. This paper systematically studied the polymerization characteristics and formation mechanism of peony-like polymer microspheres. The influence of various polymerization parameters (e.g., concentration of monomer, initiator and comonomer, time of polymerization, type of dispersion medium and mechanic stirring) on the properties (e.g., morphology, size and size distribution, etc.) of the particles has been investigated.The monodisperse polyacrylonitrile microspheres can be synthesized over a relatively wide range of monomer concentration. With the enhancement of monomer concentration, the size of polymer particles and the number of nanoflakes increased. The optimal reaction time was 2 h in the boiling medium. With the extension of reaction time, the size distribution of the particles was affected and there were kinds of particles with different morphology.The polymerization of acrylonitrile was operated in several kinds of esters with different boiling point. The polymer microspheres with different morphology and size were obtained. The results showed that the higher the boiling point of dispersion medium was, the more unapparent the extensions of the microspheres morphology became, the better the regularity became and the less the size was. In butyl acetate, the polymerization was a relatively rapid process. About 10 minutes later, the size of polymer microspheres hardly changed, and in the whole process the microspheres almost had the same morphology.Copolymerization with styrene affected greatly the morphology and size of the polymer microspheres. Adding a spot of styrene, the nanoflakes which constituted polymer particles disappeared, and the surface of the particle was only a little uneven. The larger the concentration of the styrene increased, the smoother the morphology of particles became and the better the sphericity of particles was. But increasing the styrene concentration above certain amount resulted in agglomeration. The size of particles increased with increasing the concentration of styrene, and the size distribution was better than pure polyacrylonitrile microspheres. The X-ray diffraction result indicated that adding styrene decreased the crystallinity degrees of polyacrylonitrile...