Abstract: The binding of cationic polyelectrolytes PAm·MG and P(St-Am·MG) with methyl orange(MO) and the binding of P(St-Am·MG) with MO homologue ethyl orange(EO) and orange-Ⅳ(O-Ⅳ) have been studied thermodynamically by the method of equi-librium dialysis at 25, 35, 45 and 55 ℃. The equilibrium constant K_1 and △H, △S, △G have been obtained. It has been found that the binding ability of P(St-Am·MG) is stronger than that of PAm·MG since the former contains hydrophobic group. The binding ability of dyes with P(St-Am·MG) is in the order: O-IV>EO>MO, i.e., the larger the hydrophobic group in the dyes, the stronger is the binding ability. When urea or methanol is added, the hydrophobic interaction of the polyelectrolyte and the dyes is destroyed resulting in weakening the polymer-dye binding.

Key words: Amphiphilic polymer, Methyl orange, Equilibrium dialysis, Binding, Hydrophobicity