MacromoleculesCommunications to the EditorVolume 38, Number 26 December 27, 2005 Copyright 2005 by the American Chemical SocietyComb-Coil Polymer Brushes on the Surface of Silica Nan particlesHanding Zhao,* Xiao Kang, and Li Leakey Laboratory of Functional Polymer Materials, Ministry of Education, Department of Chemistry, Nankai University, Tianjin 300071, P. R. China Received August 17, 2005Revised Manuscript Received November 4, 2005During the past decade, surface modification of inorganic Nan particles by attachment of polymer brushes has attracted much interest due to the improvement of the properties of the Nan particles, especially the dispersion and stability of the particles in various solvents.Recently, many groups reported preparation of polymer brushes on the surface of gold nanoparticles,1magneticnanoparticles,2and silica nanoparticles.3There are two principal techniques to graft polymer brushes on the surface of the inorganic particles: (1) the “grafting to” method, where the end-functionalized polymers react with the functional groups on the inorganic particle surface, and (2) the “grafting from” method, where the polymer chains grow from the initiator-modified inorganic particle surface. Because of the satiric hindrance imposed by the grafted polymer chains, it is difficult to prepare polymer brushes with high graft density on the particle surface using the “grafting to” method. How-ever, in the “grafting from” method polymer chains grow from the initiators that have been initially anchored to the particle surface, and the grafted chains will not hinder the diffusion of the small molecular monomers to the reaction sites, so the polymer brushes with higher graft density can be obtained. In recent years, there have been increasing research activities in the use of various polymerization methods to grow polymer chains on the silica particle surface. These methods include anionic polymerization,3bcat-Ni ionic polymerization,3dring-opening polymerization,3cradical polymerization,3eand atom transfer radical polymerization (ATRP).4-8Because ATRP allows better control over the molecular weight and distribution of the target polymer, much attention has been paid to these of this polymerization method in the synthesis ofpolymer brushes from a surface. Recently, Matyjasze-wskis group reported an improved ATRP method, activators generated by electron transfer (AGET) ATRP.9In a typical AGET ATRP system, an alkyl halide is used as initiator, and a transition metal complex in its ox datively stable state (e.g., Cu2+/ligand) is used as catalyst. The activator is generated by using an electron transfer to reduce the higher oxidation state transition metal. In their experiments tin(II) 2-ethylhexanoate and ascorbic acid were used as the reducing agents. The AGET ATRP method has all benefits of normal ATRP and remains tolerant to air during sanitation, so it will be very useful in the preparation of polymer brushes on the silica nanoparticles surface .In this paper we report the first synthesis of comb -coil polymer brushes on the surface of silica nanoparticles. In this approach two steps are involved. At the first step, poly(2-hydroxyethyl methacrylate) (PHEMA)brushes on the surface of ATRP-initiator-anchored silicananoparticles were prepared using ATRP. At the second step using a combination of ring-opening polymerization and AGET ATRP, poly(DL-lactate) -poly(n-butyl acryl-late) (PLA -PBA) comb-coil polymer brushes were synthesized from the backbone and the terminal site morpheme brushes, respectively. This process is illus-traded in Scheme 1. To synthesize PHEMA polymer brushes, ATRP-initiator-anchored silica nanoparticleswere prepared by a reaction of original silica particles with 3-(triethoxysilyl)polyamine and followed by an-other reaction with 2-bromoisobutyryl bromide. PHEMAbrushes were synthesized by ATRP. PLA comb and Pacolet were synthesized by a combination of ring-opening polymerization and AGET ATRP (Scheme 1). The hydroxyl groups on PHEMA chains can be used in the ring-opening polymerization of LA, and the bromide Scheme 1. Schematic Representation for the Preparation of Comb-Coil Polymer Brushes on the Surface of Silica Nanoparticles groups at the end of PHEMA chains can be used as initiators in AGET ATRP of BA. In this polymerization system, the Cu2+/bipyridine complex was used as catalyst for AGET ATRP, and tin(II) 2-ethylhexanoate was used as a reducing agent. Meanwhile, tin(II) 2-ethylhexanoate was also used as catalyst for the ring-opening polymerization of DL-lactate (LA). So the ring-opening polymerization of LA at the backbone of PHEMA chains and AGET ATRP of BA at the end of PHEMA chains were taken place in the same polymerization system (Scheme 1). In this case each monomer should independently propagate via two different mechanisms (ring opening and radical) and form different structures (comb structure at the backbone of PHEMA and coil structure at the