To promote dispersion of nano-silica in polypropylene (PP), a polymerizable foaming agent p-vinylphenylsulfonylhydrazide was synthesized and grafted onto the nanoparticles via free-radical polymerization. It was found that the grafted poly(p-vinylphenylsulfonylhydrazide) played dual role when being melt mixed with PP. The side sulfonylhydrazide groups were gasified to form polymer bubbles, leading to rapid inflation of the surrounding matrix that pulled apart the agglomerated nanoparticles, while the remaining backbone of the grafted polymer helped to improve the filler/matrix interaction through chain entanglement and interdiffusion at the interface. Mechanical tests indicated that the grafted nano-SiO2/PP composites prepared according to the above strategy were simultaneously toughened, strengthened and stiffened. Compared with conventional graft polymerization treatment where no blowing function is associated, the technique proposed in this work could significantly enhance notch impact strength of PP. (c) 2006 Elsevier Ltd. All rights reserved.