The effect of addition of acrylic acid and thioglycolic acid on the nanostructure and thermal stability of PMMA–montmorillonite nanocomposites

Poly(methyl methacrylate) (PMMA)/organophilic montmorillonite (OMMT) nanocomposites were synthesized by the in situ free radical bulk polymerization of methyl methacrylate. The effect of small amount of acrylic acid as the co-monomer and thioglycolic acid as the chain transfer agent on the nanostructure of these nanocomposites was investigated by X-ray diffraction (XRD) and small-angle X-ray scattering (SAXS) analyses. No reflection was discernible in the XRD patterns of all samples. In SAXS experiments, a great amount of small clay montmorillonite aggregates (less than 40 Å) were observed. The acrylic acid used as the co-monomer increased the affinity between the montmorillonite and the polymer, resulting in better dispersion of the montmorillonite particles. The glass transition temperature of the nanocomposites was evaluated by differential scanning calorimetry (DSC) and the thermal stability was investigated by thermogravimetric studies (TGA). As expected, the presence of the montmorillonite increased the glass transition temperature. The thermal stability of nanocomposites was distinctly higher than of pure PMMA and was increased by the presence of small amounts of acrylic acid as the co-monomer.