DIFFERENT PROTONATION BEHAVIOR OF 2 POLY(METHACRYLIC ACID) DERIVATIVES CONTAINING N-ACYLGLYCINE AND N-ACYL-BETA-ALANINE RESIDUES - THERMODYNAMIC AND FT-IR STUDIES

Two poly(methacrylic acid) derivatives containing amide and carboxyl groups in the side chain of the vinyl structure, namely poly(N-methacryloylglycine) (PMP1) and poly(N-methacryloyl-beta-alanine) (PMP2), were studied in aqueous solution at 25-degrees-C by thermodynamic (potentiometry, calorimetry, and viscometry) and spectroscopic (FT-IR) techniques together with the corresponding monomers. The basicity constants (log K) of both polymers were compared with those of other polymers with a vinyl backbone, and the anomalous behavior of PMP2 was revealed by the n value of the modified Henderson-Hasselbalch equation. The slight exothermic enthalpy changes were pH-dependent and the -DELTA-H-degrees increased with the degree of protonation-alpha for PMP1 but decreased for PMP2. The extension of hydration of the amide group revealed by FT-IR spectra was the main factor controlling the different protonation behavior of the two polyelectrolytes.