CHARACTERIZATION OF UNIMOLECULAR MICELLES OF RANDOM COPOLYMERS OF SODIUM 2-(ACRYLAMIDO)-2-METHYLPROPANESULFONATE AND METHACRYLAMIDES BEARING BULKY HYDROPHOBIC SUBSTITUENTS

The self-organization of random copolymers of sodium 2-(acrylamido)-2-methylpropane-sulfonate and methacrylamides bearing bulky hydrophobic groups, such as lauryl (LA), cyclododecyl (CD), and 1-adamantyl (AD) groups, was investigated by fluorescence, NMR relaxation, FTIR, light scattering, and small-angle X-ray scattering techniques. In aqueous solution, the hydrophobes in these polymers form clusters as a result of either intramolecular or intermolecular self-association. Studies of nonradiative energy transfer between polymers labeled with naphthalene and pyrene revealed that the polymers having the CD and AD groups formed unimolecular micelles (unimers) in a wide range of concentrations up to several weight percent, whereas the polymer having the LA groups could exist as a unimer only in a much lower concentration range (<ca. 0.2 wt %); the CD and AD residues had a strong tendency for intramolecular self-association, whereas the LA residues tended to associate intermolecularly. The pyrene labels are encapsulated within the clusters of the hydrophobes and protected from the aqueous phase as indicated by the suppression of fluorescence quenching by thallium ions. The unimers of the CD- and AD-containing polymers are extremely compact; e.g., the CD-containing polymer with M(W) = 5.1 x 10(5) forms a unimer with a mean hydrodynamic radius of 5.5 nm. Motions of the CD groups in their clusters are much more restricted than those of the LA groups as indicated by H-1-NMR relaxation times. FTIR suggests that hydrogen bonding between the spacer amide bonds may be contributing to reinforcement of the compact unimer structure.