INTERACTION OF PYRENE-LABELED HYDROPHOBICALLY-MODIFIED POLYELECTROLYTES WITH OPPOSITELY CHARGED MIXED MICELLES STUDIED BY FLUORESCENCE QUENCHING

Pyrene-labeled hydrophobically modified polyanions were prepared by te rpolymerization of sodium 2-(acrylamido)-2-methylpropanesulfonate, N-d odecylmethacrylamide (2.5-7.5 mol %), and N-(1-pyrenylmethyl)methacryl amide (1 mol %), Dynamic interactions of these polymers with mixed mic elles of II-dodecyl hexa(oxyethylene) glycol monoether (C12E6), cetylt rimethylammonium chloride (CTAC), and cetylpyridinium chloride (CPC) ( quencher for pyrene fluorescence) were monitored by fluorescence quenc hing. The charge on the micelle was varied systematically by varying t he mole fraction of CTAC (Y) in the mixed micelle. All quenching exper iments were performed at Y < Y-p, where Y-p is a critical Y at which t he polymer-micelle systems undergo macroscopic phase separation. A kin etic 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 a nd time-dependent fluorescence-quenching data. This analysis led to th e 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 marked ly increases with increasing concentration of dodecyl groups in the po lymers, even at small Y, indicating a strong enhancement of polymer-mi celle interactions by hydrophobic interactions. This large increase in the binding constant arises mainly from a large increase in the resid ence time with increase in the hydrophobe content in the: polymers, 1/ k(-1) being much more dependent on the hydrophobe content than k(1). T he results indicate that complex formation results from hydrophobic in teractions between dodecyl groups and the micelle superimposed on the effect of electrostatic farce.