The polymerization of epsilon-caprolactone (epsilon-CL) has been assessed in water using various Bronsted acids as catalysts. The reaction was found to be quantitative at 100 degrees C, leading to number-average molecular weights up to 5000 g mol(-1). The Bronsted acid-catalyzed polymerization of epsilon-CL in water was further conducted in the presence of water-soluble polysaccharides thereby affording graft copolymers. The approach enables an easy, mild access to dextran hydroxyesters. For low degree of substitution, the latter self-assembles in water to form nanoparticles. Poly(epsilon-CL)-graft-methylcellulose copolymers can also be obtained via a similar approach. It is note-worthy that the methodology reported herein is a one-step route to poly(epsilon-CL)-graft-water-soluble polysaccharides, operating in mild conditions, that is, at low temperatures, using readily available metal-free catalysts and water as a solvent. (C) 2014 Wiley Periodicals, Inc.