Heats of dilution of water-soluble polymer solutions

Abstract

In order to obtain information about the effects of water on water-soluble polymers, the heats of dilution of poly(acrylic acid)-water and poly(acrylic acid)-ethyl alcohol systems were measured at 298.15 ± 0.002 K with a specially constructed automatic microcalorimeter. The results obtained show that the heat of dilution is endothermic for the water system and exothermic for the ethyl alcohol system. In order to confirm the endothermic and/or exothermic heats of dilution of those systems, the excess volume of mixing of the systems was also measured at 298.15 ± 0.01 K using a densimeter. The sign of the excess volume for the ethyl alcohol system, but not for the water system, was in good agreement with that of the interaction heat parameter estimated by calorimetry. To obtain further information about the interaction, the interaction energies of the systems were calculated by means of ab initio molecular orbital (MO) calculations. The result obtained is about −12 kJ mol −1 for the ethyl alcohol system, suggesting that the interaction mode between poly(acrylic acid) and ethyl alcohol molecules may be based on the hydrogen bond between the COOH group in the chain of poly(acrylic acid) and the OH in the ethyl alcohol molecule from the agreement of the heats of dilution with the excess volume of mixing and/or ab initio MO calculations. However, for the water system, the interaction energy obtained is positive and its value is very large.