Synthesis and thermodynamic studies on the protonation of a new polymeric amino diacid

A linear poly(amido-amine) carrying a malonic acid moiety in the side chain of the repeating unit was synthesized and characterized. Its behaviour in aqueous solution was investigated by potentiometric, viscometric and calorimetric techniques. The basicity constant relative to the tertiary nitrogen atom decreases linearly by increasing the overall degree of protonation, while the tendency of each carboxylate ion to accept a proton is influenced by the presence of the neighbouring negative charge. The change of the basicity constants with the degree of protonation is due to entropic terms leading to energetics of protonation independent of the degree of protonation.