Countercurrent fractionation of methylol-terminated perfluoropolyoxyalkylene oligomers by supercritical carbon dioxide

•A perfluoropolyether diol (PFPE-diol) polydisperse mixture was cut into narrow fractions by supercritical carbon dioxide (scCO2).•A wider range of molecular weights than classical fractionation techniques is obtainable.•The chain length contribution to the total solubility in scCO2 was prevalent.•Non-statistical end-groups and internal units distribution in the starting mixture.•Information on the selectivity/conversion of the reactions involved in the synthesis of PFPE-diols has been acquired.