The binding of cationic surfactants by various poly(car☐ylic acid)s

Abstract

The binding isotherms of the dodecylpyridinium ion (DP +) by four polycar☐ylates, poly(fumaric acid) (PFA), poly(maleic acid) (PMA), poly(acrylic acid) (PAA), and an alternating copolymer of maleic acid and ethylene (MAE) were determined at degrees of neutralization (χ) of 0.5 and 1.0, using a potentiometric technique based on surfactantion-selective, solid state membrane electrodes. Surfactant binding by PFA and PMA show only single-step isotherms. In contrast, PAA and MAE show two-step binding isotherms, although the second binding step is weak. The binding isotherms of PFA and PMA with χ = 1.0, where the charge separation on the polymer backbone is half the value of PAA and MAE, level off at a degree of binding close to 0.5, possibly due to the effect of steric hindrance of the DP + ions at neighboring binding sites. Upon comparison of the binding isotherms in detail, we identified four types of binding site and assigned them to different chemical units contained in the chemical structures of the four polyions: CH(COO −), CH(COO −)CH 2, CH(COO −)CH(COOH) (or CH(COO −) CH 2CH(COOH)) and (CH)COO −⋯HOOC(CH) (hydrogen bonded). We found the standard Gibbs energies of binding for the four binding sites to be −20, −21, −22 and −23 kJ mol −1 respectively.