Preparation of perfluoroolefines

A process for making branched, internally-unsaturated liquid perfluoroolefins that are oligomers of tetrafluoroethylene and have an empirical formula (C2F4)n where n is an integer of 4 to 7, comprising contacting tetrafluoroethylene under anhydrous conditions with at least one fluoride which is a source of fluoride ions, said fluoride being selected from the group consisting of the normal fluorides, acid fluorides and fluorosulphinates of the metals potassium, rubidium and caesium and normal fluorides of a tetraalkylammonium ion, at a temperature of 20 DEG C to 170 DEG C in the presence of an inert solvent selected from the group consisting of dimethylformamide, dimethyl sulphoxide, N-methyl pyrrolidone and hexamethylphosphoramide, and recovering said branched, internally-unsaturated liquid perfluoroolefins from the reaction medium.