Physical and chemical characteristics of poly(maleic acid), a synthetic organic colloid analog

A relatively homogenous and easily synthesized polymer, polymaleic acid (PMA), was studied to ascertain its suitability as a model compound for humic substances. Physical and chemical properties of PMA were measured by UV/VIS, Fourier-transform infrared, and C-13 NMR Spectroscopy, high pressure size exclusion chromatography, and elemental analyses to elucidate the structural characteristics of PMA and aquatic humic substances. In terms of size, polydispersity, elemental composition, and infrared spectra, PMA most closely resembles fulvic acids derived primarily from terrestrial sources. Molar absorptivity (measured at 280 nm) and C-13 NMR spectroscopic data, however, show that PMA exhibits significantly less aromaticity than fulvic materials of similar size. In general, terrestrially derived aquatic fulvic acids possess larger percentages of aromatic carbons than either PMA or the lacustrine and subsurface fulvic acids. C-13 NMR spectra also show that aliphatic II and acetal carbons, present in several aquatic fulvic acids, are absent in PMA. Furthermore, the carboxyl carbon content of PMA is a significantly higher than that of all the humic materials used in this study. Based on these results, PMA does not resemble a unique humic substance, but rather appears to possess chemical properties common to humic materials from diverse sources.