A novel, straightforward and versatile chemical pathway has been studied to functionalize water-soluble chitosan oligomers. This metal-free methodology is based on the epoxy-amine reaction of the allyl glycidyl ether with chitosan, followed by thiol-ene radical coupling reaction of -functional mercaptans, using 4,4-Azobis(4-cyanovaleric acid) as a free radical initiator. Both reactions were entirely carried out in water. In a preliminary step, chitosan depolymerization was carried out using H2O2 in an acetic medium under 100 W microwave irradiation, optimizing the yield of water-soluble oligomers. Functionalization by six different thiols bearing alcohol, carboxylic acid, ester, and amino groups was then performed, leading to a range of functional oligochitosans with different grafting efficiencies. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 39-48