Preparation of silica/polymer hybrid microspheres and the corresponding hollow polymer microspheres with functional groups

Monodisperse functional silica/polymer core-shell hybrid microspheres were prepared by a two-stage reaction with silica grafting of 3-(methacryloxy)propyl trim ethoxysiliane (NIPS) as core and polymer as shell having various functional groups such as chloromethyl, pyridyl, carboxylic acid, hydroxyl, and ester. MPS-modified silica core was synthesized by the Stober method and subsequently grafted with MPS as the first-stage reaction. The functional polymer shell was then encapsulated over the MPS-modified silica by distillation precipitation copolymerization of divinylbenzene (DVB) as a crosslinker and comonomers with different functional groups, including chloromethylstyrene (CMSt), vinyl pyridine (VPy), methacrylic acid (MAA), 2-hydroxyethylmethacrylate (HEMA), ethyl methacrylate (EMA), ethyleneglycol dimethacrylate (EGDMA), and trimethylol propanetrimethacrylate (Trim), in neat acetonitrile with 2,2'-azobisisobutyronitrile (AIBN) as an initiator. The encapsulation of the functional polymer shell onto the MPS-modified silica core particles was driven by the capture of oligomer radicals the vinyl groups on the surface of the MPS-modified silica cores during the second-stage distillation precipitation copolymerization in the absence of any stabilizer or surfactant. The functionality and the shell thickness of the inorganic/polymer core-shell hybrid particles were controlled by the amount of DVB crosslinker and the functional comonomers during the copolymerization. The corresponding hollow polymer microspheres with various functional groups, including chloromethyl, pyridyl, carboxylic acid, and ester groups were further developed after the selective removal of silica core with hydrofluoric acid. The functional core-shell silica/polymer hybrid microspheres and the corresponding functional hollow polymer microspheres were characterized with transmission electron microscopy (TEM) and Fourier transform infrared spectra (FT-IR). Copyright (C) 2008 John Wiley & Sons, Ltd.