CHARACTERIZATION OF THE COMPLEXES OF AMPHIPHILIC POLYANIONS AND DOUBLE-CHAIN CATIONIC SURFACTANTS

Coulombic complexes of amphiphilic polyanions and double-chain cationic surfactants were prepared by adding an aqueous solution of didodecyldimethylammonium bromide (DDAB) to aqueous solutions of terpolymers consisting of sodium 2-(acrylamido)-2-methylpropanesulfonate, N-(1-adamantyl)methacrylamide (49 mol %) or N-(1-naphthylmethyl)methacrylamide (59 mol %), and N-(1-pyrenylmethyl)-methacrylamide (1 mol %). As the contents of the adamantyl and naphthyl groups in the terpolymers are sufficiently high, the parent terpolymers adopt micellelike microphase structures in aqueous solution. Both the complexes of the adamantyl and naphthyl terpolymers with DDAB were soluble in benzene, methanol, tetrahydrofuran (THF), acetonitrile (ACN), N,N-dimethylformamide (DMF), etc. H-1 NMR spectra indicated that the quantitative numbers of DDAB were ionically bound to the sulfonate sites in the parent terpolymers. Dynamic light scattering data for the complex of the adamantyl terpolymer showed that the size of the complex in THF solution ranged from 6 to 15 nm in diameter, which fairly agreed with a radius of gyration estimated on the basis of GPC data. H-1 NMR spectra, 2D-NOESY, and spin-lattice and spin-spin relaxation times for the complex of the naphthyl terpolymer in organic solution revealed that the motions of the naphthyl residues were highly restricted, while those of the DDAB residues were much less restricted. These findings imply that the micellelike microphase structure of the parent amphiphilic polyanions formed in aqueous solution remained rather intact in the complexes even though they were dissolved in organic solvents. In benzene solution, the complex was shown to be in a particularly compact form. Fluorescence emitted by the pyrenyl probes incorporated in the complexes supported these findings.