Interpolymer Association of Cholesterol Pendants Linked to a Polyelectrolyte As Studied by Quasielastic Light Scattering and Fluorescence Techniques

The association behavior of random copolymers of sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS) and cholesteryl 6-methacryloyloxyhexanoate (Chol-C 5 -MA) in 0.1 M NaCl aqueous solutions was investigated by quasielastic light scattering and fluorescence techniques to gain further insights into the structures and properties of their “intermolecularly bridged flower-type micelles” which we had proposed previously. When the Chol-C 5 -MA content in the copolymer was as low as 1 mol %, unimers were found to coexist with the interpolymer aggregates independent of the polymer concentration ( C P ) in a range 0.1 < C P < 10 g/L. However, when the Chol-C 5 -MA content was increased to 5 mol %, virtually all the polymer chains form multipolymer aggregates which can be viewed as an assembly of flower-type micelles where polymer chains are “cross-linked” via Chol associations. The aggregation number of Chol moieties was estimated to be 17−19 for the copolymer of 5 mol % Chol-C 5 -MA by a time-resolved fluorescence quenching method. Taken together with our previous results, it is concluded that each intermolecularly bridged flower-type micelle (mass ∼ 1.9 × 10 6, hydrodynamic radius ∼ 50 nm) formed from the copolymer of 5 mol % Chol-C 5 -MA is composed of 50 polymer chains in which 175 Chol groups constitute about 10 microdomains (i.e., cross-linking sites), each microdomain consisting of 17−19 Chol groups. The hydrophobic cross-links are stable enough not to be disrupted by applying shear stress up to a shear rate of 200 s - 1, but they are easily fragmented by the addition of a neutral surfactant.