al with 6 to 20 carbon atoms, a monoalkyl aromatic radical with 3 to 18 carbon atoms in the alkyl group or a di- or oligo-alkyl aromatic radical with 1 to 18 carbon atoms per alkyl group, and the total number of carbon atoms in the alkyl chains is 5 to 40, m is 0 to 20, n is 3 to 100, M is an alkali or alkaline-earth metal ion or ammonium and the degree of carboxymethylation is between 10 and 100%