High stability of thermoresponsive polymer-brush-grafted silica beads as chromatography matrices

Thermo-responsive chromatography matrices with three types of graft architecture were prepared, and their separation performance and stability for continuous use were investigated. Poly(N-isopropylacrylamide)(PIPAAm) hydrogel-modified silica beads were prepared by a radical polymerization through modified 4,4′-azobis(4-cyanovaleric acid) and N,N′- methylenebisacrylamide. Dense PIPAAm brush-grafted silica beads and dense poly(N-tert-Butylacrylamide (tBAAm)-b-IPAAm) brush-grafted silica beads were prepared through a surface-initiated atom transfer radical polymerization (ATRP) using CuCl/CuCl ₂/ Tris(2-(N,N-dimethylamino)ethyl)amine (Me ₆TREN) as an ATRP catalytic system and 2-propanol as a reaction solvent. Dense PIPAAm brush-grafted silica beads exhibited the highest separation performance because of their strong hydrophobic interaction between the densely grafted well-defined PIPAAm brush on silica-bead surfaces and analytes. Using an alkaline mobile phase, dense themoresponsive polymer brushes, especially having a hydrophobic basal layer, exhibited a high stability for continuous use, because polymer brush on the silica bead surfaces prevented the access of water to silica surface, leading to the hydrolysis of silica and cleavage of grafted polymers. Thus, the precisely modulating graft configuration of thermoresponsive polymers provided chromatography matrices with a high separation efficiency and stability for continuous use, resulting in elongating the longevity of chromatographic column.