Potentiometric and Conductometric Study of Aqueous Solutions of Lithium and Sodium Salts of Poly(thiophen-3-ylacetic acid)

The title polymer, PTAA, practically free of ester groups was obtained by oxidative polymerization of methyl thiophen-3-ylacetate and subsequent basic hydrolysis of primary polymer. Poly(thiophen-3-ylacetic acid) has been thoroughly characterized by NMR, IR, Raman, and UV/Vis spectroscopy. The polyacid behavior during neutralization titrations with lithium and sodium hydroxides, carried out under nitrogen atmosphere, has been studied by conductometry and potentiometry. Henderson-Hasselbach plots of potentiometric titration curves show a break point at pH around 6, where the curve slope drops from 1.8 (at lower pH) to a value from 1.05 to 1.3 (at higher pH values). The UV/Vis spectra monitored during back titration show: (i) monotonous decrease of both λmax and εmax as pH decreases, (ii) the presence of the isosbestic point at 401 nm that can be ascribed to conformational transition of PTAA chains, and (iii) absence of the isosbestic point at 392 nm reported previously by other authors.