Maleic acid–2-vinylnaphthalene copolymer in aqueous solution: investigation of the dissociation and fluorescence quenching

The alternating maleic acid–2-vinylnaphthalene copolymer was synthetized and characterized. The amphiphilic polyelectrolyte adopts a pseudomicellar conformation in aqueous solution. The hydrophobic microdomains are formed by the naphthalene groups and the water solubility is conferred by the hydrophilic maleic acid groups. The two-step dissociation of polyelectrolyte was studied by potentiometric titrations and the conformational transition was investigated by viscometry and fluorescence techniques. By increasing the neutralization degree over an α_N ~ 0.2, an expansion of the polymer coil takes place from a compact to a loose or extended form, but the hydrophobic microdomains formed by the naphthalene groups are present on the whole neutralization range. The investigation of the naphthalene fluorescence quenching by different transition metal ions shows an extremely high quenching efficiency by Cu²⁺ ions. The ionic strength influences the polyelectrolyte conformation and the fluorescence quenching process. The maleic acid–2-vinylnaphthalene copolymer can be used for the solubilization of polynuclear aromatic compounds or other sparingly water-soluble organic compounds or for the design of fluorescent sensors.