Surface-confined radical chain transfer: The intermediate reaction for chemically attaching polymer films on porous silica for chromatographic application

Surface-confined chain transfer reaction in free radical polymerization of different monomers leads to polymer-grafted silica particles. Porous silica is selected as the carrier of potential thiol chain transfer groups and as stationary phase in high-performance liquid chromatography (HPLC). The thiol-terminated silica and polymer over-layer-modified silica are characterized by FT-IR and Raman spectra. The chemical composite and the grafting amount of polymer on silica surface are measured by X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), etc. The grafting amount of polymer on silica surface and the molecular weight of free polymer formed in bulk solution decrease with the addition of thiol-terminated silica coincide with each other. The obtained polymethylmethacrylate (PMMA)-modified silica exhibits excellent separation capacity for three series of selected compounds, i.e. aromatic compounds and alkaloids, and displays the reversed-phase separation mechanism.