Described is the use of RO• radicals, R being a hydrogen, an alkyl group having 2 to 15 carbons, an acyl group —COR′ in which R′ represents an alkyl group having 2 to 15 carbons, or an aroyl group —COAr in which Ar represents an aromatic group having 6 to 15 carbons, for the hydroxylation, alkoxylation or oxycarbonylation of polymer or polymer mixture surfaces, the said polymers consisting in monomeric units of which at least 50% among these are aromatic units and the said RO• radicals being generated by electrochemical or photochemical methods.