Polyacrylamide was synthesized and chemically modified (PAAm) with 1,2,4,5-tetrahydroxybenzene (THB) or benzene-1,2,4,5-tetrol by applying the reaction conditions of Minisci. A degree of modification as high as 42% was obtained under the following conditions: temperature of 70–80 °C, reaction time of 3 hours and [2,5-dihydroxy-1,4-benzoquinone]-to-[AAm] ratio of 2.5. The synthesized PAAm and its modified form (THB–PAAm) were characterized by UV–Vis, Fourier transform infrared spectroscopy, 13 C nuclear magnetic resonance, differential scanning calorimetry and thermogravimetric analysis. A severe degradation of the modified PAAm was observed, as confirmed by its relatively low molecular weight. Yet, the glass-transition temperature of THB–PAAm was found to be drastically lower than that of pristine PAAm, 63.1 versus 161.19 °C. A study of copper(II) adsorption by the cross-linked PAAm and THB–PAAm resins was undertaken by varying the following parameters: pH, time, temperature, ionic strength, sorbent mass and initial copper(II) concentration. Adsorption of Pb(II) and Cd(II) by the resins and their corresponding desorption extents were estimated. A new way of crosslinking polyacrylamide and its modified form through an oxidative decarboxylation process is applied.