C(O)(=O)C=C.SCCC(O)=O.[S:12]([O-:15])([O-:14])=[O:13].[Na+:16].[Na+:17].[Na][Na].[OH:20][CH:21](S([O-])=O)[C:22]([OH:24])=[O:23].OO.[OH-].[Na+]>O.S([O-])([O-])(=O)=O.[Fe+2]>[Na:16][Na:17].[OH:20][CH:21]([S:12]([O-:15])(=[O:14])=[O:13])[C:22]([OH:24])=[O:23]
A glass reactor equipped with several feeding devices, stirrer and pH electrode was charged with 285 g of water, 210 g of vinyloxybutylpolyethylene glycol-3000 (prepared by ethoxylation of hydroxybutyl vinyl ether with 66 mol EO) and 23.3 g of isoprenylpolyethylene glycol-500 (prepared by ethoxylation of 3-methyl-3-buten-1-ol with 10 mol EO) (solution A) and was thermostated at 13° C. 35% of a second prepared, partly neutralized solution (solution B) consisting of 50 g of water and 25.4 g of acrylic acid (99%) was added to solution A over a period of 15 min in the glass reactor. Furthermore, 1.9 g of 3-mercaptopropionic acid was added to the reactor. A third solution (solution C) consisting of 5 g of a mixture of sodium sulphite, the disodium salt of 2-hydroxy-2-sulphinatoacetic acid and the disodium salt of 2-hydroxy-2-sulphonatoacetic acid (Brüggolit FF6 from Brüggemann GmbH) and 40 g of water was prepared. Thereafter, 50 mg of iron(II) sulphate haptahydrate, dissolved in a few drops of water, and 2.5 g of 50% strength hydrogen peroxide solution were added to solution A at a temperature of 13° C. At the same time, the still remaining solution B was dosed over 45 minutes and solution C over 60 minutes into the solution A. Finally, neutralization was effected with 20% strength sodium hydroxide solution. The aqueous solution of a copolymer having an average molecular weight of Mw=24 300 g/mol (determined by GPC) and a solids content of 39% was obtained.
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