Preparation of monodisperse poly(vinyl alcohol) (PVA) nanoparticles by dispersion polymerization and heterogeneous surface saponification

Monodisperse poly(vinyl alcohol) (PVA)/poly(vinyl acetate) (PVAc) nanoparticles with a skin-core structure were prepared through heterogeneous surface saponification of PVAc nanoparticles. For the preparation of PVAc nanoparticles with a uniform particle size distribution, vinyl acetate (VAc) was dispersion polymerized in a mixed solvent of ethanol and water using PVA with a low degree of saponification as a stabilizer. Increase of the amount of ethanol in media, the resulting PVAc nanoparticle size increases due to increasing solubility of VAc and oligomer PVAc. To preserve the sphericity and size uniformity of PVAc nanoparticles, we restricted saponification to the surface of the nanoparticles by using a small amount of aqueous sodium hydroxide solution. To determine the proper concentration of alkali solution for heterogeneous saponification, monodisperse PVAc nanoparticles were saponified with different concentrations of alkali solution at 25 °C for 0.5–3.0 h. The PVA/PVAc nanoparticles obtained by the heterogeneous saponification with 4 % (relative to the amount of the VAc) alkali solution for 2.0 h were uniformly shaped and monodispersed with diameter ranging from 428 to 615 nm. Transmission electron microscopy (TEM) confirmed the spherical nature and regular skin-core structure of the PVA/PVAc nanoparticles.