Vinyl polymers containing amido and carboxyl groups as side substituents, 2. Thermodynamic and fourier‐transform infrared spectroscopic studies for the protonation of poly(N‐acryloylglycine) and poly(N‐acryloyl‐6‐aminocaproic acid)

Abstract

Synthetic poly(N-acryloylglycine) (poly[1-(carboxymethylcarbamoyl)ethylene], 1a) and poly-(N-acryloyl-6-aminocaproic acid) (poly{1-[5-(carboxypentyl)carbamoyl]ethylene}, 1b) were studied in aqueous solution by thermodynamic (potentiometry, calorimetry) and Fouriertransform infrared (FT-IR) spectroscopic methods. The values of the basicity constant (log K), calculated with the Henderson-Hasselbalch equation, relative to the protonation of the carboxylate group, decreases with increasing degree of protonation (a), while the enthalpy changes are “real” for both polymers. The increased length of the lateral aliphatic chain causes a decrease in the polyelectrolyte effect and a greater entropy change ΔS° of protonation due to liberation of water molecules. At low pH the FT-IR spectra reveal a strong band at 1 628 cm−1 for polymer 1b which does not occur in the spectra of polymer 1a. At this pH the more compact macromolecular structure of 1b may favour interactions among the amido groups of several monomeric units.