Molecular-shape selectivity tuned by donor–acceptor type copolymers as organic phase in reversed-phase high-performance liquid chromatography

The copolymer with a terminal reactive group (copoly-VP17MA12) was newly designed and prepared by selecting 4-vinylpyridine (VP) as an electron-donating monomer and methyl acrylate (MA) as an electron-accepting monomer. Copoly-VP17MA12 was grafted onto porous silica particles by a silanol coupling reaction with the terminal group. Individually, poly-VP15 and poly-MA20 with a terminal reactive group were also synthesized and co-grafted onto silica (Sil-cograft-VP15MA20) to compare the effect of the copolymer-grafted (Sil-copoly-VP17MA12) and polymer co-grafted stationary phases in HPLC separation. All the polymers were characterized by 1H NMR and FT-IR analysis before grafting on silica. Polymer grafting was confirmed by diffuse reflectance infrared Fourier transform (DRIFT), elemental analysis and thermogravimetric analysis (TGA). The intra- and intermolecular interaction between monomer units in copolymer-grafted and polymer co-grafted systems, respectively was observed by DRIFT measurement. The detailed chromatographic study revealed using PAHs as solutes that remarkably higher selectivity for planar/non-planar discrimination was observed with the copolymer-grafted phase than with the co-grafted stationary phase. In this paper, it is also discussed that the selectivity enhancement by copolymer-grafting in the Sil-copoly-VP17MA12 phase can be brought through intramolecular interaction between VP and MA.