Abstract: The invention relates to a temperature-stable hydrogel comprising electrolytic water and a copolymer cross-linked to multivalent metal ions. The invention is characterized in that the copolymer contains at least structural units which are derived at up to 0.005-20% by weight from an ethylenically unsaturated phosphonic acid and alkali metal salts thereof and/or ammonia salts, up to 5-40% by weight from an ethylenically unsaturated sulfuric acid and alkali metal salts thereof and/or ammonia salts and up to 5-94.995% by weight from an amide of an ethylenically unsaturated carboxylic acid selected from the group of acrylamide, methacrylamide and/or C1-C4 alkyl derivatives, wherein the percentages are based on the total mass of the monomers used during copolymerization, and that the multivalent metal ions for cross-linking of the copolymers belong to the groups IIIA, IVB, VB, VIIIB and/or VIIIB of the periodic system of elements.

Abstract: The invention relates to a temperature-stable hydrogel comprising electrolytic water and a copolymer cross-linked to multivalent metal ions. The invention is characterized in that the copolymer contains at least structural units which are derived at up to 0.005-20% by weight from an ethylenically unsaturated phosphonic acid and alkali metal salts thereof and/or ammonia salts, up to 5-40% by weight from an ethylenically unsaturated sulfuric acid and alkali metal salts thereof and/or ammonia salts and up to 5-94.995% by weight from an amide of an ethylenically unsaturated carboxylic acid selected from the group of acrylamide, methacrylamide and/or C1-C4 alkyl derivatives, wherein the percentages are based on the total mass of the monomers used during copolymerization, and that the multivalent metal ions for cross-linking of the copolymers belong to the groups IIIA, IVB, VB, VIIIB and/or VIIIB of the periodic system of elements.