Synthesis of α, ω perfluoropolyether iodides

Perfluoropolyether (PFPE) diacyl halides of formula XCOCF2O[(CF2O)n(CF2CF2O)m]pCF2COX, with X = Cl, F and molecular weight (MW) 400–4000 g mol−1 are smoothly converted in high yields to the corresponding α, ω diiodides in the absence of solvent, employing KI or LiI at 210 °C with extrusion of CO. During the reactions, β-elimination of COF2 from the terminal difluoromethylene oxide units (CF2O, C1 unit) occurs to some extent until a tetrafluoroethylene oxide unit (OCF2CF2, C2 unit) is encountered yielding a OCF2CF2I terminus. This considerably alters the MW distribution of the final diiodide especially for low MW PFPEs. Operating in supercritical conditions of CO (scCO) or both scCO and CO2 (scCO2) on low (<600 g mol−1) MW diacyl halides, lowers β-elimination from 95 to 52 mol% if KI is used or from 43 to 30 mol% if LiI is used. With higher MW (>600 g mol−1) β-elimination is lowered from 15 to <1 mol% in scCO conditions employing KI.