Silica/poly(N,N′-methylenebisacrylamide) composite materials by encapsulation based on a hydrogen-bonding interaction

Monodisperse silica/poly(N,N′-methylenebisacrylamide) core-shell composite materials with silica as core and poly(N,N′-methylenebisacrylamide) (PMBAAm) as shell were prepared by a two-stage reaction, in which the silica core with diameter of 500 nm was synthesized in the first stage according to Stöber method. The PMBAAm shell was then encapsulated over the silica core by distillation-precipitation polymerization of N,N′-methylenebisacrylamide (MBAAm) in neat acetonitrile with 2,2′-azobisisobutyronitrile (AIBN) as initiator. The encapsulation of PMBAAm on silica particles was driven by the hydrogen-bonding interaction between the hydroxyl group on the surface of silica core and the amide unit of PMBAAm during the polymerization without modification of the silica surface in the absence of any stabilizer or surfactant. The shell thickness of the core-shell composite particle was controlled via altering the mass ratio of MBAAm monomer to silica core during the polymerization. Hollow PMBAAm microsphere was further developed after removal of silica core with hydrofluoric acid. The resultant core-shell composite and hollow microspheres were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectra (FT-IR) and elemental analysis (EA).