Salt effects on the protonation of polymethacrylate and Na+, K+, Ca2+ complex formation

The protonation of polymethacrylic acid (W∼230 000) has been studied potentiometrically [(H+)-glass electrode] in different aqueous salt solutions (NaCl, KCl, Et4NI; 0≤I≤0.5 mol dm−3) at 25°C. Measurements have been performed also for polymethacrylic acid (PMA)–CaCl2 mixtures (PMA/Ca2+=0.5–4) at I=0.1 mol dm−3 (NaCl). The potentiometric data have been analyzed first by using the three-parameters model of Högfeldt for apparent protonation constants, and then differences in different media have been interpreted in terms of complex formation. Formation constants are reported for Na+, K+ and Ca2+ complexes.