Process for production of a copolymer or a polycondensate in which the macromolecular chain is comprised of solvating units capable of inducing crystalline characteristics, units to lower the crystallinity of the copolymer of polycondensate, and eventually crosslinkable units, all the units independently of each other being of the oxyalkylene or oxy:alkenylene type, comprising (a) preparing a copolymer or polycondensate containing solvating units capable of inducing crystalline characteristics and units containing carbon/carbon unsaturation, under conditions that do not affect the unsaturation; and (b) hydrogenating at least part of the unsaturation.