Template synthesis of ordered mesoporous organic polymeric materials using hydrophobic silylated KIT-6 mesoporous silica

Abstract

Porous organic materials can be synthesized via free-radical polymerization of crosslinkable olefinic monomers within the interstices of porous templates. The synthesis process has been employed to generate ordered mesoporous structures through use of a mesoporous silica template, KIT-6. The mesoporous silica features a bicontinuously mesoporous structure belonging to the cubic Iad space group. Pore diameters of the silica could be varied over the range 3.6–7.3 nm by varying the synthesis conditions, while maintaining a constant pore wall thickness of 3.7 nm. The polymerization reaction proceeded with heating at 150 °C after initiation with α,α′-azobisisobutyronitrile. The resultant polymeric materials were characterized after template extraction using hydrofluoric acid. Characterization results demonstrated that the polymeric materials retained a cubic Iad mesoporous structure only when the template pore diameters exceeded 5 nm, even if highly crosslinkable monomers, such as divinylbenzene, ethylene glycol dimethacrylate, and trimethylolpropane trimethacrylate, were incorporated. The polymeric structure collapsed unless the template pore diameters were sufficiently larger than the distance between crosslinking points. In addition, structural integrity was maintained only if the mesopore walls were hydrophobically functionalized via silylation. Under optimal replication conditions, the ordered mesoporous polymeric materials exhibited a very narrow pore size distribution and a high specific surface area (619 m² g⁻¹) that reflected the qualities of the original silica template. Such mesoporous polymeric materials could be functionalized via copolymerization with other functional monomers or via organic reactions. The functionalized mesoporous polymers are suitable for catalytic and adsorption applications because the porous structures feature a high surface area and excellent functional group density.