Effects of Graft Densities on Separation of Bioactive Compounds on Temperature Responsive Polymer Brush Surfaces

摘要

We have systematically investigated the preparation and characterization of a series of thermo-responsive polymer-modified surfaces as chromatographic stationary phases, and have recognized polymer grafting appears to be an important determinant in these separations since graft configuration of poly(N- isopropylacrylamide) (PIPAAm) produced from different grafting methods greatly influences temperature-dependent aqueous wettability changes and solute elution behavior. We have prepared the PIPAAm grafted silica bead surfaces by mainly two kind of grafting method, ester-amine coupling methods and conventional radical polymerization. However, these methods offered little control over graft density and chain length which are believed to be two key parameters in determining the separation efficiency of biological compounds. Recently, we have prepared thermo-responsive surfaces by grafting PIPAAm to surfaces using controlled free radical polymerization techniques, such as atom transfer radical polymerization (ATRP). ATRP is an attractive polymer grafting method because it enables preparation of surfaces with well-defined polymer brushes from surface-immobilized ATRP initiators compared to the polymer brush surfaces prepared by conventional radical polymerizations. In addition, the polymer graft density also can be regulated by varying concentration of ATRP initiator on surfaces, performed by changing composition of ATRP initiator in self assembled monolayer (SAM). Thus, grafting of polymer by ATRP would clarify the effect of graft density of PIPAAm on separation of bioactive compound in the thermo-responsive chromatography. In the present report, we investigated the effects of PIPAAm graft densities on separation of bioactive compounds. PIPAAm graft density on silica bead surfaces was modulated by varying ATRP initiator concentration in SAMs. Characterization of the resulting PIPAAm brush surfaces on silica beads was investigated as a thermo-responsive aqueous chromatographic stationary phase for separation of steroids.