Interaction between water-soluble polymers and azo dyes containing fluorine atoms: Part 3. Positional effects of trifluoromethyl groups on the interaction

Abstract

The interaction between sulphonated monoazo dyes containing trifluoromethyl groups at various positions to the azo linkage and poly( vinylpyrrolidone) was investigated by means of visible absorption spectrum measurements. The positional effects of the trifluoromethyl groups on the binding of the dyes with poly(vinylpyrrolidone) are discussed using the first binding constants and thermodynamic parameters, and compared with the results for the corresponding dyes containing methyl groups. The results show that the position at which the trifluoromethyl groups are attached to the benzene ring greatly affected the binding behaviour, while such effects could not be observed in the case of the methyl groups. Furthermore, dyes containing one or two trifluoromethyl groups at the meta position to the azo group gave nonlinear van't Hoff plots, suggesting that the binding behaviour of these two dyes with polyfvinylpyrrolidone ) is unusual.