Synthesis and characterization of thermally expandable PMMA-based microcapsules with different cross-linking density

Triethylene glycol dimethacrylate (TEGDMA) crosslinked poly(methyl methacrylate) (PMMA) hollow particles with a core/shell structure containing an inert hydrocarbon (pentane) as a blowing agent were prepared by a suspension polymerization. From the synthesized microspheres, the sieved particles having sizes in the range of 44–149 μm were selected for further investigations and the effect of TEGDMA (as a cross-linker) content on the properties of synthesized particles was studied. In addition, the gel point, shell composition, particle size and its distribution, pentane content, thermal expansion properties, and particle morphology were studied. The results showed that a small change in TEGDMA concentration had a significant influence on the properties of synthesized microballoons. Kinetic studies showed that decreasing in the TEGDMA content shifted the gel point to higher reaction times. According to scanning electron microscopy (SEM) images, the shell thickness increased and particle size decreased with a decreased cross-linker concentration. The results of SEM analysis also proved the decrement of average particle size for lower TEGDMA contents. The expansion behavior of the prepared samples was investigated by means of SEM analysis. The density measurements were performed to study how the density of the particles was affected by cross-linker concentration. All samples were able to be expanded at 160 °C but the particles synthesized with lower cross-linker concentrations exhibited better expansion.