Composites of conventional ultra-high molecular weight polyethylene (UHMWPE) and nanoparticles, such as carbon nanotubes or ceramics, require special processing techniques due to the high melt viscosity of the polymer matrix. Recently, we have shown that polymerization with a single-site catalytic system in suitable reaction conditions produces "disentangled" UHMWPE that can be processed in the solid state. In this study, nanoparticles have been used as carriers for the single-site catalytic system in the polymerization of UHMWPE. The high-surface area of the nanoparticles, coupled with controlled reaction conditions, favors the growth of polyethylene chains with a reduced number of entanglements. This novel synthetic route offers several advantages: 1) the catalytic system is more stable and less fouling occurs during the polymerization reaction; 2) nanoparticles are directly embedded in an otherwise intractable polymer matrix; 3) the low amount of entanglements in the UHMWPE matrix allows the resulting composites to be processed in the solid state well below the equilibrium melting temperature in a broad temperature window, to give high strength/high modulus tapes. © 2011 Elsevier Ltd. All rights reserved.