Functionalization of Polyacrylic Acid with Tetrahydroxybenzene via a Homolytic Pathway: Application to Metallic Adsorption

Poly(acrylic acid) (PAA) was synthesized and chemically modified with 1,2,4,5-tetrahydroxybenzene (THB) or benzene-1,2,4,5-tetrol applying the reaction conditions of Minisci. A degree of modification of as high as 55% was obtained under optimal conditions: temperature of 70-80 degrees C, time of 4 h, and [DHBQ]/[AA] ratio of 1.25. The synthesized PAA and its modified form, THB-PAA, were characterized by UV-visible, FT-IR, and C-13 NMR spectroscopy. A severe degradation of the modified PAA was observed as revealed by viscometric measurements. The glass transition temperature of THB-PAA was found to be lower than that of pristine PAA, 123 versus 151 degrees C. Potentiometric titrations of PAA and its modification, and their copper (II)-complexed polymers Cu-PAA and Cu-THB-PAA with 0.1 N aqueous NaOH, showed peculiar profiles. Study of copper (II) adsorption by the crosslinked PAA and THB-PAA resins varied with the following parameters: pH, time, temperature, ionic strength, sorbent mass, and initial copper (II) concentration. Optimal copper sorption extents of 5.5 and 23mg/g for PAA and THB-PAA resins, respectively, were found for a pH of 5.4, a time of 3 h, a temperature of 45 degrees C, and an ionic strength of 0. A new way of crosslinking poly(acrylic acid) and its modified form has been conceived via an oxidative decarboxylation process.