Herein, we report a novel and facile approach to the preparation of asymmetric amphiphilic polymeric nanoparticles. Firstly, a P4VP thin film on surface of mica sheets was prepared through spin-coating. In the film, azobisisobutyronitrile (AIBN) and divinylbenzene (DVB) were solubilized. Then, the mica slides coated with the P4VP/AIBN/DVB film were immersed in an aqueous solution of N-isopropylacrylamide (NIPAM). After heating the system to 80 ℃ in N₂ atmosphere, at the early stage, free radical polymerization of DVB took place in the hydrophobic layer, which was initiated by AIBN that were mostly in the P4VP film. Due to phase separation with the P4VP matrix, the polymerization of DVB led to PDVB spheres, and the size of the PDVB spheres increased with the polymerization. When the diameter of PDVB spheres was larger than the thickness of P4VP layer or due to the migration of the PDVB spheres to water/P4VP layer interface, one side of the spheres exposed to water phase initiated the polymerization of hydrophilic monomer N-isopropylacrylamide (NIPAM). The other side of the PDVB sphere embedded in the P4VP layer was protected. This process led to the formation of amphiphilic asymmetric particles with water-soluble grafted chains on one side of a hydrophobic sphere.

Key words: asymmetric particles, interface, free radical polymerization, amphiphilic, phase separation