Synthesis of Polyacrylonitrile Based Nanoparticles via Aqueous Dispersion Polymerization

The monodisperse and controlled polymer nanoparticles have attracted much attention in academic and industrial fields. Due to small size and extremely large specific surface area, nanoparticles could be used to the fields of drug delivery system, microencapsulation, chromate graphy, catalyst, organic/inorganic hybrid materials, and templates for porous inorganic materials. The dispersion polymerization has been known for useful method to prepare micro or submicron scale monodisperse polymer particles in a single step. In this polymerization, all reaction materials are dissolved in the reaction medium at the beginning stage of the polymerization, then insoluble spherical polymer particles stabilized by steric stabilizer molecules are formed and dispersed in the reaction medium. However, this polymerization have some faults which is the number-average molecular weight (M n ) of the synthesized polymers is reported to be relatively smaller than 200,000 g/ mol. Poly(vinyl alcohol) (PVA) is a well-known protective stabilizer used in suspension polymerization. However, PVA has been rarely used in dispersion polymerization due to its very poor solubility in polymerization media, i.e., usually alcohols. The first application of pure PVA as a stabilizer dates back only to 2005 in the polymerization of vinyl acetate in which a mixture of ethanol and water was used as the polymerization medium. Since then, methyl mathacrylate and styrene have been polymerized through dispersion polymerization used pure PVA as the stabilizer in aqueous media. Acrylonitrile (AN) is a commonly used monomer for producing acrylic fiber and also acts as comonomer in the synthesis of engineering plastics because of its high chemical resistance, barrier property, and high reactivity with other monomers such as vinylidene chloride and styrene. Among the application of polyacrylonitrile (PAN), carbon fiber precursor has found significant interest due to the high tensile strength and modulus and low specific gravity. It is well known that high molecular weight and narrow polydispersity are essential requirements for high performance PAN fibers. AN is a polar organic compound and it has a substantial solubility in water (7.35 w/ v% at 20 C) compared to that of other oil-soluble monomers. In this study, poly(acrylonitrile-co-itaconicacid-co-methylacrylate) nanoparticles were successfully synthesized by aqueous dispersion polymerization using hydrophilic PVA in a water/N,N-dimethylformamide mixture media. Then the characteristic of the nanoparticles were investigated in terms of the polymerization time and concentration of stabilizer.