Thermodynamic hydrogen bonding in poly(styrene-co-acrylic acid)/poly(styrene-co-4-N,N-dimethylacrylamide) blends

FTIR study of the hydrogen bonding interactions within blends of different ratios of poly(styrene-co-acrylic acid) containing 18, 27, and 32 mol% of acrylic acid (SAA) and poly(styrene-co-N,N-dimethylacrylamide) containing 17 mol% of N,N-dimethylacrylamide (SAD-17) was carried out qualitatively and quantitatively in the temperature range varying from room temperature to 210 degrees C. Two new bands characterizing these interactions appeared in the 1800-1550 cm(-1) region at 1730 cm(-1) and 1616 cm(-1) and are attributed to liberated carbonyl group of the acidic copolymer and the associated amide carbonyl group, respectively. Equilibrium constants describing both the self-association K-2 and inter-association K-A and the enthalpy of hydrogen bonding formation in the different blends were experimentally determined using a curve fitting analysis of the infra-red spectra as a function of temperature using the appropriate equations derived from the Painter-Coleman association model. The obtained results confirm the miscibility of these blends in the considered temperature range from the negative values of the total free energy of mixing Delta G(M). Optimization of the extent of intermolecular interactions between the two polymers in these blends is investigated.