Well-defined poly(methyl methacrylate)-silica nanocomposites were produced by "grafting through" using reversible addition-fragmentation chain transfer (RAFT) polymerization. The surface of silica nanoparticle was modified covalently by attaching methacryl group to the Surface using 3-methacryloxypropyldimethylchlorosilane. Polymerization of methyl methacrylate (MMA) using the 4-cyano-4-(dodecylsulfanylthiocarbonyl)sulfanyl pentanoic acid RAFT agent, produced the PMMA-SiO2 nanocomposites. Characterization of these well-defined nanocomposites included FT-IR, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimeter (DSC), transmission electron microscopy (TEM) and dynamic mechanical analysis. These results show that the T-g values are higher and the mechanical strength of the PMMA-SiO2 nanocomposites is slightly improved when compared to bulk PMMA. Further, the molecular weight of the PMMA (up to M-n = 100,000) is controlled and the SiO2 are well dispersed in the PMMA matrix. (c) 2008 Elsevier Ltd. All rights reserved.