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

Polyoxazoline hydrogel was prepared through the coordination of the me tal ions to 2,2'-bipyridyl-branched poly(N-acetylethylenimine) (PAEI), which was synthesized from the partially hydrolyzed PAEI by the react ion with 3-{4-(4'-methyl-2,2'-bipyridyl)}propanoic acid in the presenc e 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) trichlor ide. The resulting colored gel was highly swollen in water and stable at ambient temperature for handling. In the case of nickel(II) or coba lt(II) ions, the formed intermolecular cross-linking points via the co ordination (gel state) were labile due to the rapid ligand exchange re action of the cross-linking from intermolecular to intramolecular mann er. The nickel(II) and cobalt(II) gels became soluble in a large amoun t of water within a few hours. A series of PAEIs having varying amount s of the functional groups were prepared and subjected to the cross-li nking reaction by the coordination with iron(II). The swelling degree and the stability of the gel in water depended on the content of the f unctional groups in the prepolymers. Water uptake was up to 56 multipl es of its own weight in dry state.