Process for the production of low molecular weight acrylonitrile polymers and their use

A process for the production of a water-soluble polymer predominantly containing carboxylate groups, which comprises preparing by continuous precipitation polymerization in a water/isopropanol mixture using a persulfate initiator, a polyacrylonitrile or acrylonitrile copolymer containing at least about 80% by weight of acrylonitrile units and having an average molecular weight Mw in the range from about 1,000 to 20,000 g/mol, a molecular non-uniformity of 0.3 to 2.0 and a content of terminal hydroxypropyl groups exceeding 0.5 units per molecule, removing the isopropanol to leave a suspension of the polymer with an average particle size of about 5 to 50 .mu.m obtained after removal of the isopropanol, and subjecting the suspension to continuous hydrolysis in the presence of about 50 to 110 mol-% of an alkali metal hydroxide over an average residence time of about 6 to 180 minutes at a temperature of about 120.degree. to 220.degree. C.