Thermally expandable nanocapsules obtained from surfactant-free emulsion polymerization

In this work, thermally expandable nanocapsules (TENs) with a core/shell structure were prepared by one-step surfactant-free emulsion polymerization (SFEP). Acrylonitrile (AN), butyl acrylate (BA), and methyl methacrylate (MMA) were used as the main monomers while ethylene glycol dimethacrylate (EGDMA) was employed as the crosslinking agent. In addition, toluene-p-sulfonyl hydrazide (TSH) was chosen as the blowing agent. Via SFEP, TENs were obtained without the negative effects exerted from emulsifiers and suspension stabilizers. The diameter of these synthesized nanocapsules was about 260 nm, and their core/shell structure was demonstrated by transmission electron microscopy (TEM). The thermal stability of the nanocapsules was studied by thermogravimetric analysis (TGA). In addition, the morphology of nanocapsules before and after expansion was investigated by means of scanning electronic microscopy (SEM) analysis. The thermo-expandable properties, including the start expansion temperature and the maximum expansion temperature, were tested by dilatometer (DIL). The results show that all of the samples exhibited expansion behavior while both the EGDMA concentration and shell composition had an influence on the thermo-expandable properties of the synthesized nanocapsules.