Water-soluble graft copolymers of monosaccharides, oligosaccharides, polysaccharides and their derivatives are obtained by radically initiated copolymerisation of (A) monomer mixtures of (a) more than 40-100 % by weight of at least one alpha - beta -unsaturated aldehyde having general formula (I), in which R1 stands for hydrogen or linear or branched C1-C4 alkyl, and R2 stands for hydrogen or methyl, (b) 0-60 % by weight of monoethylenically unsaturated monomers different from (a) but copolymerisable with (a), and (c) 0-5 % by weight of at least two ethylenically unsaturated monomers having no conjugated double bonds in their molecule, in the presence of (B) monosaccharides, oligosaccharides, polysaccharides, polysaccharides decomposed by oxidation, hydrolysis or enzymes, chemically modified mono-, oligo- or polysaccharides or mixtures of said compounds; and (C) one or several oxidants. The weight ratio between (A) and (B) extends from (95: 20) to (5: 80) and the weight ratio between (C) and (A) + (B) extends from (5: 100) to (50: 50). Used as builders or co-builders, these graft copolymers have good scale-inhibiting properties and are extremely biodegradable.
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