Acid functional compound

A method for producing an acid functional compound, the method comprising:

• preparing a segment by reacting a cyclic ester and a cyclic ether together in a ring-opening polymerization reaction, wherein the ring-opening polymerization reaction is started by a polymerization starter compound comprising at least one functional group selected from a hydroxyl group, a secondary amine group and a primary amine group, and
• converting the segment of with an agent to covalently link the segment to at least one acidic group selected from a phosphoric acid group, an acidic phosphoric acid ester group, a sulfonic acid group, an acidic sulfonic acid ester group, and a carboxylic acid group, the method yielding an acid functional compound comprising
• i. at least one segment comprising at least one ether unit and at least one ester unit, wherein the at least one ether unit and the at least one ester unit are connected by an ether link or by an ester link, and wherein the sum of the number of the at least one ether unit and the at least one ester unit is at least three, and wherein the at least one ether unit and the at least one ester unit-are arranged in random order, and
• ii. at least one acidic group selected from a phosphoric acid group, an acidic phosphoric acid ester group, a sulfonic acid group, an acidic sulfonic acid ester group and a carboxylic acid group, wherein the at least one acidic group is covalently linked to the at least one segment.