Poly(butyl methacrylate) (PBMA) densely grafted on a fumed silica particle consisting of primary particles with an average diameter of 14 rim, has been synthesized by surface-initiated atom transfer radical polymerization (SI-ATRP). In these syntheses, a newly designed initiator, p-(bromomethyl)benzyl 2-bromoisobutylate was used for the immobilization of the initiator moiety on the silica particle to give the densely grafted PBMA. Thus synthesized nanocomposites have exhibited unusual miscibility with poly(vinyl chloride) (PVC) through differential scanning calorimetry (DSC). The derivative DSC peaks for the composite/PVC blends were significantly different from those for the conventional PBMA/PVC blends. This interesting finding is due to a wide gradient of the PVC concentration on a microscopic scale, resulting from the densely grafted PBMA chains; the PBMA component is enriched near the surface of the fumed silica, while the PVC component is enriched far from the surface. This gradient miscible state is strongly supported by dynamic mechanical analysis. Furthermore, a synergistic effect on storage modulus was seen in the nanocomposite/PVC blends. (C) 2009 Elsevier Ltd. All rights reserved.