This investigation reports the preparation of a series of well-defined Poly(methyl methacrylate)-b-poly-(hexyl acrylate)-b-poly (methyl methacrylate) (PMMA-b-PHA-b-PMMA) triblock copolymers by Atom Transfer Radical Polymerization (ATRP). Their morphology, dynamic mechanical and tensile properties are thoroughly investigated. Phase separation is observed for all the above-mentioned triblock copolymers, which contain PMMA outer blocks in the molecular weight (M-n) range of 10,000-80,000 and PHA inner blocks with M-n in the range 20,000-40,000. The dynamic mechanical measurements essentially reveal two glass transitions and an intermediate flat rubbery plateau in between. Tensile studies indicate that as the PMMA content increases, there is an increase in tensile strength and decrease in elongation at break, which is the case for most of the thermoplastic elastomers (TPE). Eventually, the as prepared block copolymers (with PMMA content 50-80%) offer to be an effective stabilizer for preparing gold nanoparticle aggregates, the shape and size of which can be modulated by tuning the block copolymer composition. The formation of nanoparticle aggregates and their possible non-covalent interaction with the base polymer has been substantiated by UV-vis analysis, transmission electron microscopy, energy-dispersive X-ray spectroscopy, dynamic light scattering and Fourier transform infrared spectroscopy. (C) 2009 Elsevier Ltd. All rights reserved.