Polyacrylic acid (poly-A) as a chelant and dispersant

Abstract

Polyacrylic acid was synthesized in water by persulfate-initiated polymerization (solution polymerization) of glacial acrylic acid in the absence of a chain-transfer agent. The final product is odorless and colorless. Chelation for calcium ions using a calcium electrode show that our poly(acrylic acid) has a higher chelation capacity than that of existing commercial poly(acrylic acids). A design of experiments was performed to optimize the synthesis conditions to obtain poly(acrylic acid) with a high maximum chelation value. These studies also helped us to gain insight into its high chelation capacity. The chelation capacity for calcium reaches its highest values when polymerization near isothermal conditions is done ∼ 95°C with an acrylic acid concentration of ≤21 wt % and an addition time >1 h. These conditions favor higher molecular weight poly(acrylic acid) with a polydispersity ∼ 4. The dispersion properties of our poly(acrylic acid) are similar to those of the commercial ones. This dual capability of chelation and dispersion is absent in commercial chelants such as ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), and their analogs. At pH > 7, chelation of calcium by our poly(acrylic acid) is much higher than that observed with EDTA. Characterization by NMR, Raman, FTIR, and molecular modeling are included in an attempt to understand structural features that can explain the higher chelation capacity of our atactic poly(acrylic acid).