Thermally expandable nanocapsules obtained from surfactant-free emulsion polymerization

Abstract

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.

Graphical Abstract

Keywords:

• Core-shell structure
• thermal expansion
• nanocapsules
• surfactant-free emulsion polymerization

Additional information

Funding

This work was supported by the National Natural Science Foundation of China (No. 51173204, 21404121, and 51503124), the Development Fund for Special Strategic Emerging Industry in Guangdong Province, the Guangdong Natural Science Foundation (2015A030313799, 2014A030310412 and 2016A030313163), the Science and Technology Program of Guangzhou City (201510010128 and 201607010244), and the Production Education Research Project in Guangdong Province (2015B090915004, 2015B010135002).