Stability of Bivalent Metal Complexes of Streoregular Poly(methacrylic acid)

Abstract

The complex formation of bivalent metal ion, Co (II), Ni(II), Cu (II), Zn (II), or Cd (II), with isotactic or syndiotactic poly (rnthacrylic acid) (PMA) in aqueous solution was investigated by the pH titration method at 25°C and the ionic strength of 0.1. The stability constants of the PMA-metal(II) complexes were calculated by a modified Bjerrum method. The forma- tion curves of the complexes show that the Bjerrum spreading factors for isotactic PMA are smaller than those for syndiotactic PMA (Figs.3-6); in a high pH region, the complexes involving two carboxylate groups per each bivalent metal ion are more favorably formed in the case of isotactic PMA. The stability of the PMA complexes with the different bivalent cations increases in the order of Co (II) <Ni(II) <Zn(II) <Cd (II) <Cu(II), irrespective of the stereoregularity of PMA (Table 1 and 2). The overall stability constants, log β₂, indicate that the complexes with isotactic PMA are more stable than those with syndiotactic PMA (Table 2). These results can be ascribed to the more compact conformation of isotactic PMA, where the ionic groups are more closely spaced with each other.