Facile preparation of SiO₂ hybrid nanoparticles via Cu²⁺-amine redox-initiated radical polymerization

The CuSO₄-catalyzed surface-initiated conventional radical graft polymerization of electron-deficient monomers such as N,N-dimethylacryamide (DMAAm) was carried out from amino-functionalized SiO₂ nanoparticles (SiO₂–NH₂) to directly prepare hybrid SiO₂ nanoparticles (SiNPs) chemically grafted with functional poly(N,N-dimethylacryamide) (SiO₂-g-PDMAAm) in aqueous media with trimethyltetradecylammonium chloride (TTAC) added as a surfactant. The optimum reaction conditions were as follows: weight feed ratio CuSO₄·5H₂O:DMAAm:H₂O:SiO₂–NH₂:TTAC of 1:500:5,000:1,000:100 and reaction temperature at 80 °C. Spectroscopy and microscopy confirmed the successful graft polymerization and the formation of hybrid SiNPs with PDMAAm chains. Thermogravimetric analysis indicated the grafting yield could be up to 15.39 wt%. As the active radicals only formed on the SiNP surfaces, there was no free polymer in the reacting mixture. Because of the presence of PDMMAm chains, the hybrid SiO₂-g-PDMAAm nanoparticles exhibited an enhanced dispersion stability in aqueous media over the pristine SiO₂–NH₂, and a thermoresponsive settlement behavior. The parallel experiments with other electron-deficient monomers suggest that the current strategy requires less post-treatment, mild conditions and affords universal applicability.