Process for preparing modified copolymers

A process for preparing modified copolymers while substantially reducing disintegration, which copolymers contain carboxylic groups to which cations of polyvalent metals are bound which comprises

• I. reacting in a first stage a solution of
• 1. a copolymer containing a radical selected from the group consisting of (a) anhydride groups of vicinal carboxylic groups, (b) a combination of such anhydride groups with vicinal carboxylic groups, (c) a combination of said anhydride groups with other radicals capable of forming vicinal carboxylic groups and (d) a combination of said anhydride groups with vicinal carboxylic groups and with other radicals capable of forming vicinal carboxylic groups, at a temperature of 50.degree. to 180.degree. C, with
• 2. at least one alcohol containing up to 2 hydroxy groups at least one of which being a non-tertiary hydroxy group to yield a reaction product in which at least a part of the anhydride groups is converted to semiester groups, and
• Ii. reacting
• 3. the product thus obtained in the presence of water at a temperature in the range from 50.degree. to 120.degree. C with
• 4. a salt-forming compound of a polyvalent metal, the solvent present in the first stage of the reaction being compatible with said alcohol and partially miscible with water only to such an extent that two phases are formed therewith.