Hairy Hollow Microspheres of Fluorescent Shell and Temperature-Responsive Brushes via Combined Distillation-Precipitation Polymerization and Thiol−ene Click Chemistry

Abstract

Nearly monodispersed silica core−poly(N-vinylcarbazole) shell (SiO2@PVK) microspheres of 226, 235, and 244 nm in average diameters were first synthesized by surface-initiated distillation-precipitation polymerization of N-vinylcarbazole, in the presence of divinylbenzene, from the 197 nm silica template microspheres prepared by the sol−gel reaction of tetraethyl orthosilicate (TEOS) and 3-(trimethoxysilyl)propyl methacrylate (MPS). The SiO2@PVK−PNIPAM core−shell hairy microspheres (PNIPAM = poly(N-isopropylacrylamide)) were subsequently prepared by grafting the PNIPAM chains (Mn = 11 600 g/mol, polydispersity index =1.32), prepared a priori by reversible addition−fragmentation chain transfer (RAFT) polymerization, to the SiO2@PVK microspheres via the thiol−ene click chemistry. The grafting density of PNIPAM brushes on the SiO2@PVK microspheres was about 0.1 chains/nm2. Hairy hollow microspheres with a fluorescent and cross-linked PVK shell and temperature-responsive PNIPAM brushes were finally obtained, after selective removal of the inorganic silica core from the SiO2@PVK−PNIPAM microspheres by HF etching. The air@PVK−PNIPAM hairy hollow microspheres were characterized by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), fluorescence spectroscopy, and dynamic laser scattering (DLS).