Preparation Of Hollow Polyurea Microspheres Via Precipitation Polymerization

Owing to the unique inner void, hollow microspheres were applied in the fields ofcoating additives, micro-reactors and biomedicine, etc. Up to now, several effectivetechniques were developed to prepare hollow microspheres including template method,emulsion polymerization and direct surface deposition. Among these techniques, templatemethod was widely used due to its effective control of morphology and size of the hollowmicrospheres. Polyureas were one of the unique polymer materials in industry, which werederived from a chemical reaction between isocyanate and water/amine. Due to the excellentproperties of corrosion prevention, abrasion resistance and high chemical stability, polyureasstimulated versatile applications such as protective coatings and microcapsule’s wallmaterials.In this paper, by tuning the amount of monomer and reaction temperature, linearpolyurea microspheres with different size were prepared via precipitation polymerization,which using isophorone diisocyanate (IPDI) as the only monomer and acetone-water as thereaction medium. The results showed that the yield and particle size of polyurea microspheresincreased with the larger amount of IPDI while keeping the temperature constant, but themorphology of microspheres became irregular when the IPDI amount reached a certain value.If we raise temperature while keeping the IPDI amount constant, particle size of the obtainedmicrospheres increased and the yield decreased, which due to the better solubility of oligomerin higher temperature.The core-shell polyurea microspheres were prepared in two successive reaction stepswithout using the pre-formed templates. Firstly, the linear polyurea particles were obtainedvia precipitation polymerization, which subsequently been used as the templates. Secondly,the crosslinker trithylenetetramine （TETA） was dropped into the system to react with NCOon the surface of linear polymer templates in order to form crosslinked shell. The influencesof some parameters such as the amount and dropping speed of TETA, NCO concentration onthe morphology and monodispersity of the core-shell polyurea microspheres wereinvestigated. Hollow polyurea microspheres with well-preserved inner void were achieved bydissolving the core template completely in acetic acid at80°C, while the dissolution time waskept in8h. In addition, acetone was also added to well disperse the core-shell polyureamicrospheres.