Configurational effects on binding of magnesium to polyacrylic acid

✍ Scribed by Jacobson, Ada L.

• Publisher: John Wiley and Sons
• Year: 1962
• Weight: 771 KB
• Volume: 57
• Category: Article
• ISSN: 0022-3832
• DOI: 10.1002/pol.1962.1205716525

✦ Synopsis

Abstract

The effect of added Mg^++^ on the acid ionization of oxalic, citric, and polyacrylic acids is reported. The extent of ionization of the acids was varied by pretitration to various degrees with the strong base tetra‐n‐propylammonium hydroxide. The effect of subsequent addition of MgCl~2~ to these pretitrated acids was determined by pH measurements. The pH changes indicated that the strong counterion binding Mg^++^ caused release of H^+^, the amount of H^+^ released being markedly dependent on both the nature of acid and the extent to which it had been pretitrated. While the simple oxalic and citric acids behaved in a “normal” manner, H^+^ release by Mg^++^ from polyacrylic acid passed through maxima and minima as a function of degree of ionization of the acid. The maxima and minima observed can be explained by the combined effects of coulombic binding and chelation of magnesium ions, or by the effect of variation in polymer configuration on ion binding. The former explanation involves several questionable assumptions. The latter explanation can be coupled with the concept of “available” and “buried” carboxyl groups in the various possible polymer configurations. The configurational explanation appears to be the more plausible and suggests a possible new technique for the study of the effect of charge distribution in a polyelectrolyte on its configuration and on the mechanism of counterion binding.