Grafting copolymer brushes on polyhedral oligomeric silsesquioxanes silsesquioxane-decorated silica stationary phase for hydrophilic interaction liquid chromatography

A strategy is proposed to develop a stationary phase for hydrophilic interaction liquid chromatography (HILIC) using the synergistic effect of polyhedral oligomeric silsesquioxane (POSS) and copolymer brushes. Octahedral octa-aminopropylsisesquioxane (8NH2-POSS) was first bound to silica gel, followed by bromination to form a cubic initiator. Then, using acrylamide (AM) and dihydroxypropyl methacrylate (DPMA) as mixed monomers, surface initiated-atom transfer radical polymerization was conducted to prepare a stationary phase comprising cubic copolymer brushes with amide and diol groups. The characterization of the stationary phase confirmed the successful synthesis of Sil-NH2-POSS/Poly(AM-co-DPMA). The chromatographic properties were investigated using nucleosides, organic acids and β-agonists to find that our designed column has superior hydrophilic property, better separation performance compared with classical HILIC columns consisting of diol- or amino-modified silica. The systematic investigation of the retention mechanism and separation selectivity using various types of polar compounds revealed that Sil-NH2-POSS/Poly(AM-co-DPMA) follows a mixed-mode retention composed of HILIC and electrostatic interactions. Besides, it exhibits good column efficiency and stability. The role of 8NH2-POSS in the separation was evaluated by comparing the performance of Sil-NH2-POSS/Poly(AM-co-DPMA) and poly(AM-co-DPMA)-modified silica without 8NH2-POSS. In conclusion, our designed based on POSS and hydrophilic copolymer brushes can contribute to the development of HILIC separation materials with enhanced performance.