Interaction of pyrene-labeled hydrophobically modified polyelectrolytes with oppositely charged mixed micelles studied by fluorescence quenching

Pyrene-labeled hydrophobically modified polyanions were prepared by terpolymerization of sodium 2-(acrylamido)-2-methylpropanesulfonate, N-dodecylmethacrylamide (2.5-7.5 mol %), and N-(1-pyrenylmethyl)methacrylamide (1 mol %), Dynamic interactions of these polymers with mixed micelles of II-dodecyl hexa(oxyethylene) glycol monoether (C(12)E(6)), cetyltrimethylammonium chloride (CTAC), and cetylpyridinium chloride (CPC) (quencher for pyrene fluorescence) were monitored by fluorescence quenching. The charge on the micelle was varied systematically by varying the mole fraction of CTAC (Y) in the mixed micelle. All quenching experiments were performed at Y < Y(p), where Y(p) is a critical Y at which the polymer-micelle systems undergo macroscopic phase separation. A kinetic model was developed to estimate the binding constant (K) (when K = k(1)/k(-1)), association late constant (k(1)), and lifetime of bound micelle on the polymer (residence time) (1/k(-1)) from steady-state and time-dependent fluorescence-quenching data. This analysis led to the following results: K increases with Y because both k(1) and 1/k(-1) increase with Y, k(1) being more dependent on Y than 1/k(-1). K markedly increases with increasing concentration of dodecyl groups in the polymers, even at small Y, indicating a strong enhancement of polymer-micelle interactions by hydrophobic interactions. This large increase in the binding constant arises mainly from a large increase in the residence time with increase in the hydrophobe content in the: polymers, 1/k(-1) being much more dependent on the hydrophobe content than k(1). The results indicate that complex formation results from hydrophobic interactions between dodecyl groups and the micelle superimposed on the effect of electrostatic farce.