INTERACTION BETWEEN WATER-SOLUBLE POLYMERS AND AZO DYES CONTAINING FLUORINE-ATOMS .2. SULFONATED MONOAZO DYES CONTAINING PENTAFLUOROANILINE AS A DIAZO COMPONENT

The interaction between sulphonated monoazo dyes derived from pentafluoroaniline as a diazo component and poly(vinylpyrrolidone) was investigated by means of visible absorption spectrum measurements. To elucidate the effects of the fluorine atoms, the corresponding dyes using aniline as diazo component were also investigated. In the difference absorption spectra for sodium pentafluorophenylazo-2-hydroxy-3,6-naphthalenedisulphonate, no distinct isosbestic point was observed at the ratio of the polymer concentration based on the monomer mol unit to the dye of more than 300 and multiple binding equilibria were apparent. On the other hand, the difference absorption spectra for the solutions with ratio less than 300 showed distinct isosbestic points, resulting in a single equilibrium. Using the first binding constants, the enthalpy change, and the entropy change, the effects of the fluorine atoms of the dye molecules and also of those of cosolutes (NaCl and NaSCN) are discussed.