Hyperbranched polysiloxysilane (HBPS) terminated by the vinyl functional group was synthesized by the self polymerization of AB, monomer, 1,5-divinyl-1, 1,3,5,5-pentamethyltrisiloxane, in the presence of the platinum catalyst. The terminal vinyl group was converted to 2-hydroxyethyl by the reaction with 9-BBN as the hydroboration reagent. The terminal function was then modified to the 2-bromoisobutyryl group by the reaction of hydroxyl group with 2-bromoisobutyryl bromide. The obtained HBPS possessing the 2-bromoisobutyryl terminal group was immobilized on the silica surface by mixing the silica bead and HBPS in hexane. Block copolymer of HBPS and poly(N-isopropylacrylamide) (PIPAAm) was synthesized by the atorn transfer radical polymerization (ATRP) using 2-bromoisobutyryl terminated HBPS as a macroinitiator. The molecular weight of the block copolymer was M-n = 23,500 and M-w/M-n = 1.31. Graft polymerization of N-isopropylacrylamide on the silica surface was carried out on the 2-bromoisobutyryl terminated HBPS immobilized silica bead using ATRP. The PIPAAm grafted silica bead was applied to the column packed material for temperature-responsive HPLC. Two kinds of steroids, hydrophilic and hydrophobic, were successfully separated by the HPLC system. (c) 2006 Elsevier Ltd. All rights reserved.