Synthesis Of Iron Oxide Rods Coated With Polymer Brushes And Control Of Their Assembly In Thin Films

We investigated the surface-initiated atom transfer radical polymerization (SI-ATRP) of methyl methacrylate (MMA) using monodisperse rod-type particles of iron oxide, beta-FeOOH. The slow hydrolysis of iron(III) chloride yielded monodisperse beta-FeOOH rods with an average length-to-width ratio, L/W, of 6 (L = 210 nm and W = 35 nm on average). The surfaces of the beta-FeOOH rods were modified with a triethoxysilane derivative as an ATRP-initiating site, namely, (2-bromo-2-methyl)propionyloxypropyl triethoxysilane. The SI-ATRP of MMA, mediated by a copper complex, was performed using the initiator-coated beta-FeOOH rods in the presence of a sacrificial free initiator. Well-defined poly(methyl methacrylate) (PMMA) brushes with molecular weights of up to 700 000 could be grafted on the beta-FeOOH rods with a surface density as high as 0.3 chains/nm(2). The resultant polymer-brush-afforded hybrid rods exhibited high dispersibility in various solvents for PMMA without forming aggregates. Thin films were prepared by dip-coating from a suspension of the hybrid rods, and the rods were oriented in a specific direction in the films. The arrangement of the rods could be controlled by varying the chain length of the polymer brush and the withdrawal speed during the dip-coating process.