Preparation and evaluation of surface-grafted block copolymers and random copolymers via surface-initiated atom transfer radical polymerization for hydrophilic/ion-exchange stationary phases

Mixed-mode chromatographic (MMC) stationary phases must be functionalized with at least two functional groups to yield multiple interactions. The present study proposed a novel approach of grafting copolymers with monomers with different properties via surface initiated-atom transfer radical polymerization (SI-ATRP) for the development of MMC stationary phases. In the synthesis, block copolymers and random copolymers containing sodium 4-styrenesulfonate (NASS) and dimethylaminoethyl methacrylate (DMAEMA) units were controllably grafted onto a silica surface via SI-ATRP for the preparation of hydrophilic/ion-exchange stationary phases. Upon investigation of their retention behaviors under different chromatographic conditions (i.e. water content, salt concentration and pH in mobile phase, column temperature) compared to a typical diol column, both the block and random copolymer stationary phases presented mixed-mode retention mechanisms involving hydrophilic and ion-exchange interactions. Furthermore, various solutes, such as basic beta-agonists, strong polar nucleosides, organic acids, and a real sample of safflower injection, were employed to evaluate the separation selectivities of the stationary phases; similar selectivities and good separation efficiencies were achieved on the two copolymer columns. In conclusion, the method of surface-grafted copolymers via SI-ATRP possesses potential for further applications in the development of various MMC stationary phases.