Thermally Modulated Cationic Copolymer Brush on Monolithic Silica Rods for High-Speed Separation of Acidic Biomolecules

Poly(N-isopropylacrylamide (IPAAm)-co-2-(dimethylamino)ethylmethacrylate(DMAEMA)-co-tert-butylacrylamide (tBAAm)), a thermoresponsive-cationic-copolymer, brush-grafted monolithic-silica column was prepared through surface-initiated atom transfer radical polymerization (ATRP) for effective thermoresponsive anion-exchange chromatography matrices. ATRP-initiator was grafted on monolithic silica-rod surfaces by flowing a toluene solution containing ATRP initiator into monolithic silica-rod columns. IPAAm, DMAEMA, and tBAAm monomers and CuCl/CuCl₂/Me₆TREN, an ATRP catalytic system, were dissolved in 2-propanol, and the reaction solution was pumped into the preprepared initiator modified columns at 25 °C for 16 h. The constructed copolymer-brush structure on monolithic silica-rod surface was confirmed by X-ray photoelectron spectroscopy (XPS), elemental analysis, scanning electron microscopy (SEM) observation, and gel permeation chromatography (GPC) measurement of grafted copolymer. The prepared monolithic silica-rod columns were also characterized by chromatographic analysis. The cationic copolymer brush modified monolithic silica-rod columns were able to separate adenosine nucleotides with a shorter analysis time (4 min) than thermoresponsive copolymer brush-modified silica-bead-packed columns, because of the reduced diffusion path length of monolithic supporting materials. These results indicated that thermoresponsive cationic copolymer brush grafted monolithic silica-rod column prepared by ATRP was a promising tool for analyzing acidic-bioactive compounds with a remarkably short analysis time.