Effect of Monomer Composition on the Core–Shell Structure and Expansion Performance of Thermally Expandable Microspheres

This study investigated the effect of different monomer compositions of acrylonitrile (AN) and methyl methacrylate (MMA) on the synthesis and expansion performance of thermally expandable microspheres (TEMs). TEMs with different monomer ratios, specifically AN to MMA ratios of 100:0, 90:10, 80:20, and 70:30, were synthesized via free radical suspension polymerization. The inner morphology, crystallinity, blowing agent encapsulation efficiency, and expansion ratio of the microspheres were analyzed using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and other characterization techniques. The results showed that as the MMA content and reaction time increased, the internal structure of the microsphere shell became more uniform, and its thickness increased. Notably, the P(AN:MMA)(90:10) microspheres exhibited the lowest expansion temperature and the highest expansion ratio. This study provides a theoretical basis for the further optimization of TEM synthesis processes.