SYNTHESIS OF BIPYRIDYL-BRANCHED POLYOXAZOLINE AND ITS GELATION BY MEANS OF METAL COORDINATION

Polyoxazoline hydrogel was prepared through the coordination of the metal ions to 2,2'-bipyridyl-branched poly(N-acetylethylenimine) (PAEI), which was synthesized from the partially hydrolyzed PAEI by the reaction with 3-{4-(4'-methyl-2,2'-bipyridyl)}propanoic acid in the presence of dicyclohexylcarbodiimide. Concentrated solution of 2,2'-bipyridyl-branched PAEI gave polyoxazoline gel in a good yield by the treatment with metal salts such as iron(II) sulfate, or ruthenium(III) trichloride. The resulting colored gel was highly swollen in water and stable at ambient temperature for handling. In the case of nickel(II) or cobalt(II) ions, the formed intermolecular cross-linking points via the coordination (gel state) were labile due to the rapid ligand exchange reaction of the cross-linking from intermolecular to intramolecular manner. The nickel(II) and cobalt(II) gels became soluble in a large amount of water within a few hours. A series of PAEIs having varying amounts of the functional groups were prepared and subjected to the cross-linking reaction by the coordination with iron(II). The swelling degree and the stability of the gel in water depended on the content of the functional groups in the prepolymers. Water uptake was up to 56 multiples of its own weight in dry state.