Because of advantageous features such as shorter reaction times, greater yields, limited generation of by-products and relatively easy and straightforward scale-up, microwave-assisted synthesis has become a very appealing tool in organic synthesis. Conversely, its implementation in the context of the synthesis of biomaterials for biopharmaceutical applications has been more limited. The present work reports on the fast and efficient microwave-assisted synthesis of poly(ethylene glycol) (PEG)-initiated poly(epsilon-caprolactone) diols (PCL) by the ring-opening polymerization (ROP) of epsilon-caprolactone using stannous octanoate as catalyst. Since the PEG content in the synthesized copolymers was extremely low (0.2-1.9%), products were highly hydrophobic and displayed the intrinsic thermal properties of pure PCL. As opposed to the more time-consuming conventional thermally-driven synthesis that usually demands 2-3 h, the microwave technique resulted in intermediate to high molecular weight PEG-PCL derivatives within 10-15 min. The influence of different parameters affecting the synthetic process, namely monomer-to-initiator ratio, reaction time, catalyst concentration and the presence, type, and concentration of solvent were thoroughly investigated. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 1321-1329, 2011