The synthesis and characterization of a new oligo(hexafluoropropylene oxide)-b-oligo(ethylene oxide), oligo(HFPO)-b-oligo(PEG), diblock co-oligomer are presented. First, the model reactions dealing with the radical addition of 1-iodoperfluorohexane (C 6 F 13 I) onto allyl alcohol and allyl-O-PEG-OCH 3 were optimized in terms of the choice of the initiator (azobisisobutyronitrile [AIBN], tert-butylperoxypivalate [TBBPi], and benzoyl peroxide [BPO]) and of the solvent, temperature, and time. Allyl-O-PEG-OCH 3 was obtained from the etherification of ω-hydroxy-PEG with allyl bromide. End-capping of oligo(HFPO) with PEG was successfully achieved by the radical addition of 1-iodoperfluoropropyl-2-oligo(hexafluoropropylene oxide) [oligo(HFPO)-CF(CF 3 )CF 2 I] onto allyl-O-PEG-OCH 3 using the best conditions of the model reactions. Although TBPPi failed and led to oligo(HFPO)-isobutyl iodide, AIBN and BPO yielded oligo (HFPO)-CH 2 CHICH 2 -oligo(PEG). The selective reduction of the latter compound led to oligo(HFPO)-b-oligo(PEG) in 77% yield, the surface tension properties of which were compared to those of commercially available ammonium perfluorooctanoate (APFO) and perfluorooctanoic acid (PFOA). Its critical micelle concentration was 0.04 g mol −1 . All models, intermediates, and diblock co-oligomers were characterized Introduction Polyfluorinated compounds (PFCs) are useful chemicals involved in a wide range of products. Among them, molecules that bear both fluorinated hydrophobic moieties and hydrophilic parts, called "surfactants", 1-4 are valuable compounds. Surfactants are being used in more than 200 applications 5-10 ranging from the protection of surfaces (textile, paper, carpets, masonry, metal, and leather), as stimulating fluids for oil recovery, fire-fighting foam, skin protection from chemical agents, soil and stain-repellents, plane hydraulic fluids, 1,11 paints, lubricants, electroplating, photographic emulsifiers, pressure sensitive additives, pharmaceuticals, and insecticides, or are involved in cosmetic formulations. Perfluorooctanoic by 1 H, 19 F, and 13 C NMR spectroscopy as well as matrix assisted laser desorption ionization (MALDI) and atmospheric pressure solids analysis probe (ASAP) time-of-flight mass spectrometry (TOF-MS).