Well-Defined Silica-Polymer Core-Shell Hybrids and Polymer Hollow Structures: Synthesis, Characterization and Application

Abstract

Well-defined inorganic/polymer core-shell hybrids and polymer hollow micro-/nanostructures are of great interest because of their diverse applications in chemistry, materials, biomedicine and nanotechnology. The aim of this work was to develop a simple and general approach to the fabrication of functional inorganic/polymer core-shell hybrids and polymer hollow nanostructures with unique morphology and decorated surface functions via a combination of traditional techniques, such as sol-gel chemistry, distillation-precipitation polymerization and living radical polymerization with the newly developed `click? chemistry. The as-prepared polymer hollow micro-/nanospheres (single shell, double shell, rattle-type and hairy hollow particles) could further been explored as drug delivery vehicles in drug delivery systems (DDSs) and nanoreactors in confined catalytic reactions.

First of all, narrowly-distributed (or monodispersed) poly(methacrylic acid) (PMAA) hollow microspheres with stimuli-responsive properties have been fabricated from the corresponding silica/polymer composite hybrids via a combined distillation-precipitation polymerization and sol-gel chemistry. By such means, hybrid microsphres with alternating SiO2/PMAA layer were further produced by sol-gel process and distillation-precipitation polymerization. Hollow PMAA microspheres with double-shell structures and PMAA-PNIPAM double shelled hollow microspheres were obtained by selective removal of silica core and inter-layer from the alternating SiO2/PMAA/SiO2/PMAA hybrids in HF solutions. The obtained double-shelled PMAA and PMAA-PNIPAM hollow particles could exhibit a reversible volume change to the stimuli of the environmental medium

Subsequently, a serial of rattle-type hollow nanospheres with a polymer shell or mesoporous silica shell and various metal nanocore (gold, silver, or anatase titania) were synthesized using the metal/silica core-shell particles as templates. These well-defined rattle hollow hybrid nanospheres, comprising of the two nanostructured functional materials, can be used for confined catalytic reactions as a nanoreactor system. Furthermore, the as-synthesized Ag@air@PMAA hybrid nanorattles with a Ag nanocore, PMAA shell and free space in between. The as-synthesized Ag@air@PMAA hybrid nanorattles were explored as a nanoreactor system for confined catalytic reduction of 4-nitrophenol. The rate of catalytic reaction can be further regulated by controlling molecule diffusion in and out of the stimuli-responsive PMAA shell through the simple variation of environmental stimuli, such as salt (NaCl) concentration of the medium.

Lastly, combination of the robust alkyne-azide, thiol-ene `click? chemistry with the living radical polymerization technique has been explored and exhibited a novel strategy for the fabrication of polymer brush-decorated inorganic/polymer core-shell hybrids and polymer hollow spheres. The as-prepared hollow nanospheres with hairy surfaces and multiple functionalities could improve the particle properties and be explored for biomedical applications as a probe for cell imaging and as a vehicle in drug delivery systems (DDSs).