The process for the scission of high molecular weight perfluoropolyethers having neutral end groups obtained from photo-oxidation processes of perfluoroolefins, or fluorination of hydrogenated polyalkylene oxides, or by polymerization with opening of the partially fluorinated oxetane ring, the scission being carried out in the presence of catalysts selected from the group consisting of fluorides, oxyfluorides and oxides of transition metals, or selected from the group consisting of Al, Sn, and Sb, at temperatures ranging from 150.degree. to 380.degree. C. The scission process leads to the formation of low molecular weight perfluoropolyethers having neutral and acid end groups, the perfluoropolyetheral acids being subjected to conversion reactions in order to obtain functionalized perfluoropolyethers. The products can be used as operative fluids for high vacuum pumps.