Supereritical carbon dioxide has been of great interest in various areas of chemical science and engineering during the last decade. In this thesis, the properties of poly (methyl methacrylate) (PMMA)/silica nanocomposites with different surfactant and filler concentrations synthesized through in-situ polymerization in supercritical carbon dioxide were investigated. In addition, ferromagnetic nano-particles were synthesized and functionalized for the preparation of nanocomposites. The thermal stability and surface morphology of PMMA/iron oxide nanocomposites synthesized in supercritical carbon dioxide were first studied in the work.

The scanning electron microscopy micrographs show that higher surfactant concentration results in higher number density of polymeric nanocomposite particles and better dispersion of nano-particles in the polymeric composites. Higher concentration of silica nano-particles in the composites results in excessive particle agglomeration. The cause of agglomeration is due to the MPS molecules on different particles react with each other. A better thermal stability of the composites, as revealed by thermal gravimetric analyses and differential scanning calorimetry analyses, was observed due to the enhancement of the surfactant and filler interactions. Surprisingly, composites with PMMA grafted particles did not show an anticipated drastic improvement of the mechanical properties. This may result from the plasticizing effect of the stabilizer used in the dispersion polymerization.