Abstract: The invention relates to a process for preparing products containing polymer chains in which a linear prepolymer or polymer contains at least one free acid group at each chain and is reacted with an alkoxide of a metal having a valence of more than 2, such as zirconium, titanium or cerium, possibly in the presence of a non polar solvent, the alkoxide of the metal having a valence of more than 2 being used in such a quantity that the alkoxide functions are in excess with respect to the stoichiometric amount of the acid functions carried by said linear prepolymer or polymer, the reaction mixture being stirred in the presence of humidity until a product is obtained wherein the hydrogen atoms of the free acid end groups of the prepolymer or polymer are substituted by an atom of the metal (M) which is itself linked to another atom of said metal by M-O-M linkages. The invention relates also to the products containing a prepolymer or polymer .alpha.,.omega.