Preparation and catalytic use of silica-polymer core–shell microspheres with imidazolium-styrene copolymer shells

Silica-polymer core–shell microspheres with imidazolium-styrene copolymer shells were prepared by polymerization of acidic ionic liquids with styrene in the presence of 3-mercaptopropyltrimethoxysilane (MPTMS)-modified silica, in water–ethanol mixed solvent. It was found that the thickness of the copolymer shells and the amounts of ionic liquids contained in the shells depended largely on reaction parameters such as the emulsifier, and the type and mole fraction of acidic ionic liquid. Unlike the neat imidazolium-styrene copolymers, the silica-polymer core–shell microspheres were insoluble in organic solvents. Moreover, they retained the properties of the imidazolium-styrene copolymers while affording improved mechanical strength due to their core–shell structure. The core–shell microspheres can be used as efficient catalysts for acetalization of carbonyl compounds with methanol under mild reaction conditions.