Synthesis and characterization of silica nanoparticles functionalized with multiple TEMPO groups and investigation on their oxidation activity

Abstract

A series of novel silica nanoparticles functionalized with multiple TEMPO groups were synthesized using a novel, efficient and versatile protocol. First, the amino-functionalized silica nanoparticles (SN-NH₂) were obtained using an improved one-pot hydrolysis and co-condensation procedure of APTES and TEOS agents, and further modified with 2-bromoisobutyryl bromide for macro-initiator (SN-Br) by amidation reaction. Then, the polymer grafted silica nanoparticles (SN-g-PGMA) with a dense shell layer of PGMA side-chains were realized via the surface-initiated atom transfer radical polymerization (SI-ATRP) procedure in a controlled manner. Subsequently, the azido groups were introduced onto PGMA side-chains by the quantitative ring-opening reaction of an epoxide with a sodium azide agent, and the TEMPO groups were further attached by efficient “Click” chemistry with propargyl-TEMPO for the target SN-g-(PGMA-TEMPO). The evidence for the successful synthesis of target polymers and intermediates was sufficiently provided by FT-IR, EPR, XPS, TEM, ¹H NMR, and TGA measurements. As an important task, the catalytic activity of the synthesized SN-g-(PGMA-TEMPO) was evaluated by the oxidation of benzylic alcohols according to the Anelli protocol, as well as the excellent efficiency, stability and recyclability of the catalyst were also confirmed.