Well-defined polymer-Mg(OH)(2) nanocomposites were prepared by atom transfer radical polymerization (ATRP). The ATRP initiators were covalently attached to the Mg(OH)(2) by esterification of 2-chloropropionyl chloride with hydroxyl group. The amount of polymer grafted from Mg(OH)(2) can be controlled using a different catalyst system and adding a small amount of polar solvent. The well-defined diblock copolymer, consisting of poly(styrene) (PS) and poly(methyl methacrylate) (PMMA) were synthesized. The products were characterized by nuclear magnetic resonance, Fourier transform infrared, differential scanning calorimetry, and thermal gravimetric analysis. The morphologies of PS/PMMA and PS/PMMA/Mg(OH)(2)-g-PS-b-PMMA blends are compared by using a scanning electron microscope. (c) 2006 Wiley Periodicals, Inc.