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Abstract

Bridged, water-soluble copolymers are obtainable by (A) copolymerization of a monomer mixture of (a) from 50 to 99 mol % of acrylamide and/or methacrylamide, (b) from 50 to 1 mol % of a monoethylenically unsaturated monomer containing actual groups and (c) from 0 to 20 mol % of monomers which differ from (a) and (b), in the presence of a polymerization initiator under conditions such that the acetal groups of the monomers (b) undergo virtually no hydrolysis, (B) hydrolysis of the acetal groups of the monomers (b), present as copolymerized units in the copolymers (A), (C) condensation of the copolymers (B) containing aldehyde groups at a pH above 5, at most to a degree such that the resulting condensates are still water-soluble and (D) stopping of the condensation reaction by adding acid until the pH reaches 3 or less, and are used as paper stock additives in papermaking for increasing the wet strength of paper.

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