Reversible thermoresponsive aggregation/deaggregation of water-dispersed polymeric nanospheres exhibiting structural transformation

Crystalline polymeric nanospheres composed of poly{stearyl methacrylate (SMA)-co-poly(ethylene glycol) monomethacrylate (PEGm)}s were prepared by the dispersion radical polymerization of SMA and PEGm in an ethanol/water solution. Scanning electron microscopy showed that the nanospheres were highly spherical, and had a narrow size distribution. Electron spectroscopy for chemical analysis and X-ray diffraction studies of the nanospheres suggested a core-corona-type structure; the hydrophilic PEGm corona accumulated on the nanosphere surface, while the hydrophobic SMA core formed a layered structure. Heat treatment caused a melting of the SMA layers, but successive cooling allowed it to re-form. Accompanying this reversible order-disorder transition, the nanospheres also showed a reversible aggregation/deaggregation behavior in their water-dispersion state.