Extraction of iron(II)-tris(1,10-phenanthrolinato) chelate into the polymer phase formed from an aqueous solution of poly(N-isopropylacrylamide)

When an aqueous solution of a water-soluble polymer, poly(N-isopropylacrylamide) (PNIPAAm), was heated above 32°C, the polymer became insoluble, and then formed paste-like precipitates (polymer phase) having a very small volume fraction. A water-soluble cationic chelate, iron(II)-tris(1, 10-phenanthroline) [Fe(phen)3]2+, was well extracted into the polymer phase as the ion-pair with perchlorate. On the basis of the volume fractions of the aqueous and polymer phases, the logarithmic distribution constant of the ion pair evaluated was 2.53±0.05, promising high efficiency in the concentration of the ion pair. Based on the spectra of 1-(4-hydroxyphenyl)-2, 4, 5-triphenylpyridinium hydroxide inner salt and 1-ethyl-4-carboxymethoxypyridinium iodide in the polymer phase, the polar parameters, ET(1) and Kosower′s Z values of the PNIPAAm phase were 257 and 333kJ mol-1. These results suggest that the solvent properties of the polymer phase correspond to those of alcoholic solvents, such as methanol or ethanol. The high extractability of the [Fe(phen)3]2+(ClO4-)2 ion pair was ascribable to the polar properties of the polymer phase.