Synthesis of tetra-layer polymer composite microspheres and the corresponding hollow polymer microspheres with Au nanoparticles functionalized movable cores

Hollow poly(ethyleneglycol dimethacrylate) (PEGDMA) microspheres with Au nanoparticle functionalized movable cores were prepared by selective removal of the sandwiched silica mid-layer from the corresponding poly(ethyleneglycol dimethacrylate-co-methacrylic acid)/poly(ethyleneglycol dimethacrylate-co-vinylpyridine)@gold/silica/PEGDMA (P(EGDMA-co-MAA)/P(EGDMA-co-VPy)@Au/SiO2/PEGDMA) tetra-layer composite microspheres, in which the Au nanoparticles were stabilized by the pyridyl groups on the surface and gel-layer of P(EGDMA-co-MAA)/P(EGDMA-co-VPy) particles during the reduction of HAuCl4 with sodium borohydride. The tetra-layer polymer composite microspheres were synthesized via the combination of distillation precipitation polymerization for the preparation of the polymer core and outer shell layer together with the modified Stöber sol–gel process for the formation of the sandwiched silica mid-layer. The primary results indicated that the Au nanoparticle functionalized movable cores enabled the hollow polymer microspheres to act as efficient catalysts for the reduction of 4-nitrophenol to 4-aminophenol with sodium borohydride as the reductant.