Organic solvent treatment and physicochemical properties of nanoporous polymer–SBA-15 composite materials

Mesoporous polymer–silica composites are attractive new materials because these systems can combine the advantages of highly porous silica and the vast functional diversity of organic polymers in a single robust structure. This contribution deals with the effects of organic solvent treatment on the physicochemical properties of mesostructured polymer–SBA-15 silica nanocomposites. For this study, two distinct reference mesoporous nanocomposites were prepared using a previously reported surface-confined polymerization technique, e.g., poly(styrene)(PS)–SBA-15 composite and poly(2-hydroxyethyl methacrylate)(PHEMA)–SBA-15 composite. The resulting materials are treated either with chloroform or toluene under heating for a prolonged period of time (24 h). Both materials are characterized prior and after solvent treatment by nitrogen physisorption at −196 °C, thermogravimetry and Attenuated Total Reflection Infra-Red (ATR-IR) spectroscopy. In general, solvent stability is excellent for both types of composite, even for low cross-linking degree of the polymer. Our data reveal that a treatment of mesoporous PHEMA–SBA-15 with chloroform or toluene has a minor, but reproducible, effect on the composite material in terms of porosity. Here, a reorganization of the polymer layer–silica interface seems to occur to some extent, which is leading to slight variation of the intrawall porosity. As a consequence, an increase of the thermal stability is clearly observed, with, however, no marked difference in the mean mesopore diameter. On the other hand, the PS–SBA-15 composite treated with the same solvents shows higher specific surface area values and an improved homogeneity in terms of polymer coating compared to untreated materials, especially for composites synthesized using benzoyle peroxide as the polymerization initiator. However, no increase in thermal stability is observed in this case.