A straightforward and very efficient pathway has been reported for the synthesis of a functional derivative of epsilon-caprolactone, i.e. 5-ethylene ketal epsilon-caprolactone. This new monomer has been homopolymerized and copolymerized with epsilon-caprolactone in a well-controlled manner, strongly suggesting absence of any side reactions. Deacetalization of the polyester chains is complete and reduction of the ketone groups into hydroxyl groups as well. No chain scission is observed to occur in the course of these two derivatization reactions. Thus, aliphatic polyesters bearing either ketone pendent groups or hydroxyl pendent groups can be easily prepared, which raises new application prospects. These materials proved to be easily redispersed in an aqueous medium. They form stable colloidal nanodispersions (e.g. 100 nm). These suspensions are stable more than 48 h at room temperature and may be viewed as potential drug colloidal vectors with a core-shell like structure. Different types of reactive groups on the surface of these nanoparticulate vectors are indeed available to the binding of species selected for molecular recognition and drug targeting. For instance, the well-known reactivity of ketones toward primary amines is a direct route to attach peptides onto biodegradable and biocompatible aliphatic polyesters. Poly(epsilon-caprolactone) with hydroxyl groups reactive toward triethylaluminum provides a macroinitiator for lactone and lactide polymerization, so that biodegradable and biocompatible functional comb, graft, and dendritic aliphatic polyesters can now be synthesized.