Core-shell structured MCM-48-type silica-polymer hybrid material synthesis and characterization

In the current study, a core-shell structured material of MCM-48-type mesoporous silica nanoparticles (MSNs) and cross-linked poly(N-isopropylacrylamide) homopolymer and its copolymer with methacrylic acid was synthesized. The polymer was preferentially grafted on the outer surface of silane linker-functionalized MSNs based on free radical polymerization. The successful chemical grafting of the polymer on the silica surface was confirmed by FTIR, NMR, TG, and elemental analyses. The polymer contents of the hybrid particles vary from 18 to 40 % as determined by thermogravimetric and elemental analyses. The polymer content was tailored by varying different reaction parameters including monomer concentration, linker content/type, and reaction time. Well-defined uniform core-shell structured spherical particles with an average particle size of 367 +/- 25 nm and shell thickness of 29 +/- 8 nm were observed in TEM analysis. According to XRD and nitrogen physisorption studies, the ordered mesopore structure of the core MCM-48-type MSNs was maintained after an extended polymer grafting process and surface coverage with a high content of polymer. No significant pore blockage was observed in porosimetry analysis. More than 75% of specific surface area, 68% of total pore volume, and the mean mesopore diameter were retained after successful grating of polymer on the outer silica surface. The pore volume thus can provide enough space to encapsulate high contents of cargo molecules for applications. The narrow pore width distribution of the main mesopores of silica determined by PALS analysis corresponds to the N-2 sorption analysis and further confirms the uniformity of the mesopores.