Synthesis of poly(styrene-co-acrylonitrile) copolymer brushes on silica nanoparticles through surface-initiated polymerization

Abstract

In the present investigation, silica nanoparticles have been coated with poly(styrene-co-acrylonitrile) (SAN) copolymer brushes synthesized via surface-initiated atom transfer radical polymerization (ATRP). In the initial step, silica nanoparticles were functionalized with triethoxysilane-based ATR initiator, 6-(2-bromo-2-methyl) propionyloxy hexyl triethoxysilane. Successful formation of the covalent linkages between ATRP initiator and silica nanoparticles is further corroborated using thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The surface initiated ATRP of the styrene and the acrylonitrile mediated by a copper complex was carried out using the initiator fixed silica nanoparticles in the presence of a sacrificial (free) initiator. The polymerization is preceded in a living manner in all examined cases, producing nanoparticles coated with well-defined poly(styrene-co-acrylonitrile) (SAN) brushes with molecular weight in the range of 12–22 kDa. SAN-grafted silica nanoparticles were characterized using TGA which showed significant weight loss in the temperature range of 340–420 °C confirming the formation of the polymer brushes on the surface with graft densities in the range of 0.109–0.190 chains/nm2. Successful formation of the SAN copolymer brushes are further characterized by FTIR and proton nuclear magnetic resonance spectroscopy techniques. Differential scanning calorimetric studies revealed that the SAN copolymer grafted onto silica nanoparticles exhibits higher glass transition temperatures than free SAN copolymers. Transmission electron microscopy and dynamic light scattering studies revealed that the SAN copolymer-grafted silica nanoparticles showed relatively fine dispersion in organic solvents such as tetrahydrofuran, when compared to bare silica nanoparticles.