Magnetically responsive hierarchical magnetite/silica/poly（ethyleneglycol dimethacrylate-co-4-vinylpyridine） （Fe3O4/SiO2/P（EGDMA-co-VPy）） tri-layer microspheres were used as stabilizers for gold metallic nanoeolloids as a facilely recoverable catalyst with the reduction of 4-nitrophenol to 4-aminophenol as a model reaction. The magnetic microsphere stabilized gold metallic nanocolloids were prepared by in situ reduction of gold chloride trihydrate with borohydride as reductant via the stabilization effect of the pyridyl groups to gold nanoparticles on the surface of the outer shell-layer of the inorganic/polymer tri-layer microspheres.
Hollow poly（divinylbenzene-co-methacrylic acid） （P（DVB-co-MAA）） microspheres were prepared by the selective dissolution of the non-crosslinked poly（methacrylic acid） （PMAA） mid-layer in ethanol from the corresponding silica/PMAA/P（DVB-co-MAA） tri-layer hybrid microspheres, which were afforded by a three-stage reaction. Silica/PMAA core-shell hybrid microspheres were prepared by the second-stage distillation polymerization of methacrylic acid （MAA） via the capture of the oligomers and monomers with the aid of the vinyl groups on the surface of 3-（methacryloxy）propyl trimethoxysilane （MPS）-modified silica core, which was prepared by the Stober hydrolysis as the first stage reaction. The tri-layer hybrid microspheres were synthesized by the third-stage distillation precipitation copolymerization of functional MAA monomer and divinylbenzene （DVB） crosslinker in presence of silica/PMAA particles as seeds, in which the efficient hydrogen-bonding interaction between the carboxylic acid groups played as a driving force for the construction of monodisperse hybrid microspheres with tri-layer structure. The morphology and the structure of silica core, silica/PMAA core-shell particles, the tri-layer hybrid microspheres and the corresponding hollow polymer microspheres with movable silica cores were characterized by transmission electron microscopy （TEM）, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy （XPS）.
Monodisperse hollow polymer microspheres having various functional groups on the shell-layer, such as carboxylic acid, pyridyl and amide, were prepared by two-stage distillation precipitation polymerization in neat acetonitrile in the absence of any stabilizer or additive, during which monodisperse poly（methacrylic acid） （PMAA） afforded from the first-stage polymerization was utilized as the seeds for the second-stage polymerization. The shell layer with different functional groups was formed during the second-stage copolymerization of either divinylbenzene （DVB） or ethyleneglycol dimethacrylate （EGDMA） as crosslinker and the functional comonomers, in which the hydrogen-bonding interaction between the carboxylic acid group of PMAA core and the functional groups of the corresponding comonomers, including carboxylic acid, amide and pyridyl, played an essential role for the formation of monodisperse core-shell functional microspheres. The hollow polymer microspheres were then developed after the subsequent removal of PMAA cores by dissolution in ethanol under basic condition. Transmission electron microscopy （TEM） and scanning electron microscopy （SEM） were used to determine the morphology of the resultant PMAA core, functional core-shell microspheres and the corresponding hollow polymer microspheres with different functional groups. FT-IR spectra confirmed the successful incorporation of the various functional groups on the shell layer of the hollow polymer microspheres.
