PMMA/mesoporous silica nanocomposites: effect of framework structure and pore size on thermomechanical properties

Mesoporous forms of silica (MS) with different framework structures and pore sizes, including hexagonal MCM-41 (2.4 nm), cubic MCM-48 (1.9 nm), hexagonal SBA-15 (7.0 nm) and mesocellular silicafoam MSU-F (24.8 nm), were examined as functional additives in the preparation of poly(methyl methacrylate) (PMMA)/mesoporous silica nanocomposites made by in situemulsion polymerization and compression molding. All of the composites at 5 wt% loadings of MS, exhibit improved thermal stability, an elevated glass transition temperature, and an enhanced storage modulus in comparison to the pristine polymer. MSU-F silica with the largest framework pore size provides the composite with the best improvement in thermomechanical properties. In general, the improvements in thermal stability and modulus diminish with decreasing framework pore size of the silica additive. For composites made from MCM-41 and MCM-48 silicas with similar pore sizes, the 3D MCM-48 structure provided superior benefits. The improvements in thermomechanical properties for the composite are attributed to the confinement of polymer in large pore channels, especially those with a 3D structure.