A humic-acid-like polycondensate produced with no use of catalyst

The synthesis and physicochemical characterization of a water soluble humic-acid-like polycondensate (HALP), which mimics fundamental physicochemical and spectroscopic properties of natural humic acids is presented. The polymer can be synthesized under ambient O(2) by oxidative co-polymerization of gallic (GA) and protocatechuic (PA) acid at pH >9, with no need for a catalyst. Solid state (13)C NMR spectra for GA-PA-HALP show that ring-opening reactions of GA, PA monomers are involved in GA-PA-HALP formation. EPR spectroscopy shows that GA-PA-HALP contains stable phenol-based radicals, with pH-dependent concentration. The H-binding profile of GA-PA-HALP follows the NICA-Donnan model, with two sets of distributed pK(a) values in the range 4-6 corresponding to carboxyl groups, and 7-9 corresponding to phenolic groups, as in natural HA. GA-PA-HALP bears a permanent negative charge Q(0)=-2.3 equiv kg(-1) which is higher than the literature Q(0) values of -1 to -2 equiv kg(-1) observed for natural HAs. A critical comparison of the present data with literature data is provided.