Influence of Graft Density of Poly (N-Isopropylacrylamide)-Grafted Silica on Separation Performance

Poly (N-isopropylacrylamide) (PNIPAAm)-grafted silica beads with variable graft densities were prepared by atom transfer radical polymerization (ATRP). The ATRP initiator on the surface of silica was prepared through the aminopropyl silica and 2-bromoisobutyryl bromide. Acetyl chloride was used to control the graft density. The content of carbon, hydrogen, and nitrogen were measured by elemental analyzer. The graft ratio was characterized by thermogravimetric analysis and the molecular weight of the polymer was determined by GPC analysis. The retention behavior of five steroids under different temperature was studied. Furthermore, the influence of temperature and graft densities to the separation of steroid compounds was investigated. The results indicated that graft density had a significant influence on the separation efficiency. Thinner PNIPAAm chains on hydrophilic silica surface can achieve the stationary phase with enhanced temperature sensitivity and better separation property.