Living anionic surface-initiated polymerization (LASIP) of a polymer on silica nanoparticles

To demonstrate living anionic surface-initiated polymerization (LASIP) on silica nanoparticles, the initiator precursor 1,1-diphenylethylene (DPE) was functionalized with alkyldimethylchlorosilane and grafted onto silica particle surfaces. n-BuLi was used to activate the DPE, which allowed the anionic polymerization of the styrene monomer to proceed in benzene solution. A high-vacuum reactor was used to allow polymerization from the surface of silica particles under anhydrous solution conditions. The dispersion of the DPE functionalized silica particles showed a distinct red color indicating an activated nanoparticle-DPE-n-BuLi complex suitable for anionic polymerization. The degree and mechanism of polymerization were determined based on characterization of the grafted and detached polystyrene chains using thermogravimetric analysis, size exclusion chromatography, NMR, and Fourier transform infrared spectroscopy. In addition, atomic force microscopy and X-ray photoelectron spectroscopy were used to characterize the polymer-coated nanoparticles. The importance of activation of the grafted initiator, control of aggregation, and removal of the excess n-BuLi for high molecular weight formation is emphasized. While the polydispersities are broader compared to those obtained by solution polymerization of a free initiator, a living anionic polymerization mechanism is still observed.