Potentiometric and conductometric titrations were used to study the dissociation behaviour of poly(propene-co-maleic acid) and poly(propene-co-maleic acid) modified with various contents of taurine (2-aminoethanesulfonic acid) in salt-free solution. Copolymers of propene and maleic acid with different molecular weights were titrated with LiOH, NaOH, and KOH. The influence of molecular weight on pK(a) is ascertainable in both the first and second dissociation step. Of the various alkali metal cations studied, lithium had the most significant effect on the dissociation behaviour. The acidic strength decreased in the order lithium > sodium greater than or equal to potassium. After insertion of sulfonic acid groups into poly(propene-co-maleic acid), the influence of strong acidic groups on the dissociation behaviour of carboxylic groups was studied. The contents of taurine were 10, 25, and 50 mol%. The second dissociation step was analyzed in this case. The pK(a) values increased with increasing content of taurine for titrations with LiOH and KOH, but not NaOH. When NaOH was used, the pK(a) decreases if the polymer was modified with 10% taurine. Higher taurine contents had no influence on the magnitude of pK(a). The results demonstrate the strong influence of short-range electrostatic interactions on the dissociation behaviour of weak polyacids.