Facile synthesis of functional silica/polymer composite materials and hydrophilic hollow polymer microspheres

Abstract

Monodisperse functional silica/polymer coreshell composite materials with silica as core and hydrophilic polymer with various functional groups, such as amide, carboxylic acid, hydroxyl, and pyridyl group, as shell were facilely prepared by a two-stage reaction, in which the silica core with diameter of 179 nm was synthesized in the first-stage reaction according to the Stöber method. The functional polymer shell was then encapsulated onto the silica core by distillation-precipitation copolymerization of N,N′- methylenebisacrylamide (MBAAm) as crosslinker and hydrophilic comonomers with different functional groups, including N-isopropylacrylamide, methacrylic acid, 2-hydroxyethyl methacrylate, and 4-vinylpyridine, in neat acetonitrile with 2,2′-azobisisobutyronitrile as initiator. The encapsulation of the functional polymer shell onto the silica core particles was driven by the hydrogen-bonding interaction between the hydroxyl group on the surface of silica core and the amide unit of MBAAm crosslinker as well as the functional groups of the comonomers during the distillation-precipitation polymerization without modification of the silica surface in absence of any stabilizer or surfactant. The shell thickness of the composite can be controlled by MBAAm fraction in the monomer feed during the polymerization. Hydrophilic hollow polymer microspheres with various functional groups, including amide, carboxylic acid, hydroxyl, and pyridyl, were further developed after selective removal of silica core with hydrofluoric acid. The functional core-shell silica/polymer composites and the corresponding functional hollow microspheres were characterized with transmission electron microscopy, Fourier transform infrared spectra, and dynamic light scattering. © 2008 Wiley Periodicals, Inc.