Determination of charge density of anionic polyacrylamide flocculants by NMR and DSC

New methods are suggested for the determination of the charge density of acrylamide/acrylate copolymers.¹³C nuclear magnetic resonance spectroscopy was used to determine the comonomer ratio by comparing the peak intensities of the methine carbon in acrylamide and acrylate monomers. Results were compared with those obtained by conductometric and potentiometric titration and were found to be in good agreement. Differential scanning calorimetry was employed to determine the glass transition temperatures (T _g) of the copolymers. A master curve was established by plottingT _g versus charge density of the copolymers previously determined by NMR and conductometric titration. Compositions of poly(acrylamide-co-acrylate) samples can thus be determined by measuring theT _g and reading the percent composition directly from the master curve.