The influence of cations on the dissociation behaviour of copolymers of propene and maleic acid and their modified products with taurine in salt-freesolution

Potentiometric and conductometric titrations were used to study the dissoci ation 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 differe nt 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 stre ngth decreased in the order lithium > sodium greater than or equal to potas sium. After insertion of sulfonic acid groups into poly(propene-co-maleic a cid), the influence of strong acidic groups on the dissociation behaviour o f carboxylic groups was studied. The contents of taurine were 10, 25, and 5 0 mol%. The second dissociation step was analyzed in this case. The pK(a) v alues 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 poly mer 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 we ak polyacids. (C) 1999 John Wiley & Sons, Inc.