A method [method (P FH for the synthesis of a mixture of polymers [polymer mixture (FH CH2F)] comprising a partially fluorinated polyether backbone having two chain ends, each of said chain ends being linked to an opposite side of said backbone, wherein each of the first chain end [end (Re 1)] and the second chain end [end (Re 2)] is independently selected from the group consisting of -CR H 1 R H 2 -OC(=O)F, -C(=O)F, and -CR H 1 R H 2 F, with R H 1 and R H 2, equal to or different from each other, are each independently H or a C 1 -C 6 hydrocarbon group; said process comprising: Step: a step of contacting: - at least one perfluoro compound [compound] comprising at least two acyl-fluoride groups; and - at least one hydrogenated compound [compound] comprising at least two fluoroformate groups of formula -CR H 1 R H 2 -O-C F, in the presence of at least one fluoride-containing compound, to provide a mixtures of polymers [polymer (FH FOR)] comprising a partially fluorinated polyether backbone having two chain ends, wherein said backbone comprises recurring unit(s) derived from said at least one compound alternately arranged with recurring unit(s) derived from said at least one compound, and wherein each of said chain ends, equal to or different from each other, is selected from the group consisting of a group -CR H 1 R H 2 -OC(=O)F and a group -C(=O)F; Step: a step of heating said polymer (FH FOR) obtained in step above at a temperature exceeding 120°C, preferably in the range from 130°C to 210°C, for a duration of at least 4 hours and in the presence of a fluoride-containing compound, typically in the presence of a fluoride-containing compound comprising at least one of (i) a metal fluoride of formula MeF y, with Me being a metal having y valence, y being 1 or 2, in particular NaF, CaF 2, AgF, RbF, CsF, KF; and (ii) an (alkyl)ammonium fluoride of formula NR HN 4 F, with each of R HN, equal to or different from each other being, independently, a H or an alkyl group, in particular tetrabutylammonium fluoride, so effecting the thermolysis of at least a fraction of the chain ends of polymer (FH FOR) of formula -CR H 1 R H 2 -OC(=O)F to groups -CR H 1 R H 2 -F, to provide the polymer mixture (FH CH2F). Step: a step of contacting: - at least one perfluoro compound [compound] comprising at least two acyl-fluoride groups; and - at least one hydrogenated compound [compound] comprising at least two fluoroformate groups of formula -CR H 1 R H 2 -O-C F, - at least one perfluoro compound [compound] comprising at least two acyl-fluoride groups; and - at least one hydrogenated compound [compound] comprising at least two fluoroformate groups of formula -CR H 1 R H 2 -O-C F, in the presence of at least one fluoride-containing compound, to provide a mixtures of polymers [polymer (FH FOR)] comprising a partially fluorinated polyether backbone having two chain ends, wherein said backbone comprises recurring unit(s) derived from said at least one compound alternately arranged with recurring unit(s) derived from said at least one compound, and wherein each of said chain ends, equal to or different from each other, is selected from the group consisting of a group -CR H 1 R H 2 -OC(=O)F and a group -C(=O)F; Step: a step of heating said polymer (FH FOR) obtained in step above at a temperature exceeding 120°C, preferably in the range from 130°C to 210°C, for a duration of at least 4 hours and in the presence of a fluoride-containing compound, typically in the presence of a fluoride-containing compound comprising at least one of (i) a metal fluoride of formula MeF y, with Me being a metal having y valence, y being 1 or 2, in particular NaF, CaF 2, AgF, RbF, CsF, KF; and (ii) an (alkyl)ammonium fluoride of formula NR HN 4 F, with each of R HN, equal to or different from each other being, independently, a H or an alkyl group, in particular tetrabutylammonium fluoride, so effecting the thermolysis of at least a fraction of the chain ends of polymer (FH FOR) of formula -CR H 1 R H 2 -OC(=O)F to groups -CR H 1 R H 2 -F, to provide the polymer mixture (FH CH2F).