THE INTERACTIONS OF POLYACRYLIC ACID, POLYMETHACRYLIC ACID, POLYACRYLAMIDE AND POLYMETHACRYLAMIDE WITH SOME DISPERSE DYES

Abstract

The interactions of polyacrylic acid (PAA), polymethacrylic acid (PMA), polyacrylamide (PAAm) and polymethacrylamide (PMAm) with some disperse dyes such as azobenzene, p-hydroxyazobenzene and p-aminoazobenzene were studied by an equilibrium dialysis method at 5°, 15° and 25°C.It was found that PMA displays a strong binding affinity toward these disperse dyes and on the contrary PMAm does a weak one. In the cases of PAA and PAAm no similar phenomena were observed. An addition of urea to PMA solution promoted a marked decrease in the binding ability.The results are interpreted in terms of the interaction of these dyes with partially hydrophobic tightly coiled chains of PMA, which are stable in aqueous solution and not in aqueous urea solution.The binding isotherm between the dyes and PMA was exhibited by the Langmuir one, so the thermodynamic parameters, free energy change, enthalpy change and unitary entropy change, can be calculated from the Klotz's equation. The free energy change and the enthalpy change obtained in this work are all negative and the unitary entropy change is large positive. The favorable binding process, therefore, involves two main contributions, an entropy gain and an exothermic interaction. Comparing the effect of the entropy term with that of the enthalpy one, the former is larger than the latter in the course of the binding process. In particular azobenzene which is the least polar compound has larger positive entropy change.From the above data it was deduced that the large positive unitary entropy change may be attributed to the hydrophobic interaction between the dyes and PMA.The viscosity of PMA, PAA, PAAm and PMAm in aqueous solution and aqueous urea solution was measured and discussed in some detal.